Florence Grovida Gardening

Fokm Of The Plantcell 1

The wood of the species of Mammiltaria differs little from this. At first sight it appears to consist of an entirely uniform tissue of somewhat extended cylindrical cells, which are distinguished by a most delicate spiral band projecting far into the cell (fig- 50. B). By greater observation upon kmgitudinu! and transverse sections of the cells in which the spiral

fibres project less into the cells, it will be found that they are in communication with one another, and allow air to pass through (fig- 50. A af B a\ This is the simplest form of the so-called vessel,

In another way a simple kind of wood is formed in Carotinea minor* II is extremely light and soft (like cork), and consists of regular paren-cbyma-cells, slightly elongated and somewhat porous, and of individual rows of much broader and longer, cylindrical, and clearly porous cells (called vessels ), standing in open communication with one another. Very similar to this is the wood of Bomhax pentandra (figs, 51, 52-), where we find, between the parenchymatous cells, individual, long, but tolenibly thin-walled, prosenchyma-cells (figs. 51t 52, b). From this to the ordinary wood a transition is formed by some wood in my possession from the

" vi* Tramverw section of the wood of Cycai rrvoluta, Br Longitudinal section of the samt?, parallel to the medullary rays, a, In both figures medullary ray cells» Tim mfflit elongated cells hare upon their walls innumerable large pore*.

At Transverse section uf the wvod of MumrHillQria qvadrbfritui. Bt longitudinal section of the same, parallel to the bark, a and cf Spirally formed plates inside Ilia cells : these cells contain only air* 6, Medullary ray cells.

cover of a Chinese casket. At a cursory first glance the transverse section (fig. 53.) appears to exhibit clearly defined annual rings. More accurate research shows that the dark stripes which, as the most external part of an annual ring, appear, are not connected, but form isolated transverse bands between the two medullary rays. These transverse

Transverse section of the wood of Bombax pentandra. The entire wood consists 6k thin* walled but porous parenchyma (c), in which individual thick-walled wood-cells (6) are scattered. Small medullary rays, consisting of individual rows of cells, pass through the wood at pretty regular distances. In the under half of the section, the cell-walls become imperceptibly thicker, by which the boundaries of the two annual rings are clearly indicated. Single or in pairs, porous cells, lying on one another, pass through the wood (c).

" Longitudinal section of the same wood. a, Porous vessels, fr, Wood-cells, c, Parenchyma.

M Transverse section of wood from a Chinese casket, with a low magnifying power. At first sight, the dark transverse bands might be regarded as the boundaries of the annual rings. They are not, however, connected together, and each extends between the medullary rays. The small space marked at x is strongly magnified at fig. 54., where it will be seen that the dark bands are formed out of small stripes of wood-cells, which alternate with a thin-walled porous parenchyma (c). Between the wood-cells and the medullary rays there exists also a layer of thin-walled parenchyma-cells, Between the wood-cells may be observed radial rows of somewhat broader and smaller thick-walled wood-cells. The thin-walled medullary ray cells (6) are also porous. Fig. 55. is a longitudinal section, parallel to the medullary rays; and the letters a, 6, c indicate the same parts as in fig. 54. Large porous vessels are seen in fig. 53., which are not represented in the other figures.

bands consist exclusively of prosenchyma (figs. 54. a, 55. a), whilst the wood between which they lie consists of very regular, not much extended, thin-walled, and porous parenchyma (figs. 54. c, 55. c).

From the foregoing remarks and observations it will be seen that what are called vessels are unessential modifications of the cellular tissue, and care should be taken that no erroneous impression be conveyed by the once generally received term of " vascular bundles." Such bundles may

The opposite of this is the extremely light and porous wood of the various species of Avicennia, which consists almost entirely of very broad porous vessels, whose interstices are filled with small porous parenchyma-cells (fig. 56.).

Lastly, the great mass of most wood consists of longitudinal, thick-walled prosenchyma-cells, and, to a greater or less extent, of smaller porous vessels (figs. 57,58.).

• Transverse section of the wood of Avictnnia. The wood consists entirely of very broad porous vessels, together with very small thin-walled parenchymatous cells.
• Transverse section of the very heavy and thick wood of Mahonia nepalensts. The entire mass consists of very thick-walled wood-cells (c> and broad porous vessels (6). The cells of the medullary rays («) are very thick-walled, and scarcely to be distinguished from the wood-cells.
• Longitudinal seetion of the same, a, b, c, correspond with fig. 55. d, the cut cells of a large medullary ray.

be seen without vessels in the longitudinal tissue of many Crj/p/tK/amiat as in the Mosses, also amongst thu l?Jianeroffftmia* in Mayvca jïueia-til is, some aperies of Potamofjeton* in Najas, Caulinia, and firato-p/iyllum ; in short, in all plants growing under water* or which are nourished from their surface mid not their root a. The terra " vessel" has misled botanists, and it is lime that we should be apprised of the fart that there is as much difference between the so-culled vegetable vessels nud those of uni mais, us there is between vegetable and animal wings and reproductive germs. The vessels of plant* play but ïl very subordinate part in the functions of vegetable life, and, bo tar from being special organa for the circulation of the fluids of plants, they are themselves the Ust produced results of such movements of the sap, and the first parts to become filled up and impervious to the admission of the juices circulating in the plant. Vessels are often found wanting in entire plants, and the most impartant parts of plants, as in the gemmules and filaments, whilst in other plants closely related to these they are found present These views of the doctrine of the vascular bundles 1 first propounded in Wiegtnann's Archîv for IB39 (Bd. L S. 220,) *

5 27, /?. Tissue of tfte Liber (Tela JUrotOf Bastgcwebe> This is formed of cells so long that they cannot be regarded as cclls superimposed upon one another, but as fibres lying clo^c to one another. The walls of tlicee cell* are strong, often thïckeued so as to exclude the transmission of light, without exhibiting a clear configuration of the deposit layers, They arc mostly soft and flexible* These cells seldom present themselves individually in the pith and the bark : they arc more frequently seen in bundles (liber-bundles), in the visible nerves (vcin^) of flat small leaves, in the projecting angles of stems, and very frequently in the neighbourhood of the vascular bundles on the external side of the cambium i itt the last it is especially callcd liber,

F, LibElt CELLS of Apocynaccœ and Asclepiadacece* These an; peculiarly long, seldom branched cells, with thickcned walls* which often exhibit very delicate spiral fibres crossing each other, hi some spots their cavity is entirely obliterated, îvhilat in others they arc swollen and vesicular, and contain a true milky juice,

G- Milk Vessels ( Vasa lactcscentia)t are longitudinal cells, frequently branched in all directions- Sometimes then: walls arc thin and homogeneous ; at other times* cspecially from age, they arc thickened by layers, and marked in a spiral manner (as in the leafless Fupkorbiaceœ)^ They couUin a colourless or variously coloured milky juice-

There are few departments of botany that ufTer more unanswered questions, and that demand greater research, than the subjects of the three preceding paragraphs.

The fibres of the liber in the youngest parts of the hud in which I hey can be seen a™ very abort, almost spindle-shaped, celle* which He with their sharp ends pushed between each other, so that as the part to which they belong increases in length, so do they increase alft0, but are brought

• This papor is aho printed in Schleiden'a BuUnittht Boitrmg«, vol. i. p, £!>, has bwn translated in Taylor** Scientific Mtiimirs, nrnl by the Sydenham Swii'ty»—Ta^k*, into closer contact, always pressing more and more upon each other, until they are quite parallel. They probably originate in parenchymatous cells, in the same way as prosenchyma. Between them and the longitudinal parenchymatous cells, there are a number of transition forms, and in many cases it is difficult to say to which form a particular tissue may belong. Such intermediate forms are very frequent in monocotyledons in the neighbourhood of vessels; they are also seen in dico tyledons, as in some of the Cactacece (fig. 59,). As they approach the character of shorter cells, the configuration of the walls, with pores or sharply defined layers, is evident (figs. 60, 61.).

If we regard the pointing at both ends and the thickness of the deposit layers as essential characters of liber-cells, then the branched cells discovered by me* in the ovary of some Aroidece (in Momtera and Scindapsus), and in the pith of Rhizophora Mangle (fig. 63.), belong to them.

Ordinarily the liber-cells are so long, that the whole of them cannot be seen by a strong magnifying power (fig. 62.), and, next to the cells of some species of Chara and the pollen tubes of some plants, are the longest cells which present themselves in the vegetable kingdom. I have measured liber-cells from 4 to 5" in length, but these are probably not the

• Wiegmann's Arcbiv, 1839, vol. i. p. 231. ; Schleiden, Botanische Belt rage, yoI. i. p. 42.

" Ad intermediate form between liber- and parenchyma-cells (a), from the bark of the root of MaxiUaria atropurpurea.

m A liber-fibre, short, thick, and porous, from the China rcgia.

41 Transverse section of three liber-fibres and some parenchyma-cells from the China rcgia (Cinchona $crobicuIaia Humb. Yellow Bark.) The liber-cells show beautifully the deposit-layers and the porous canals.

® Upper end of a liber-fibre from the Tilia europaa.

m A branched liber-cell from the pith of Rhizophora Mangle.

longest. The branched liber-cells (fig. 63.), on account of their branching, are included in the following forms.

Upon the origin of the liber-cells of Apocynaceœ and Asclepiadaceœ no observations have been made : only thus much is certain, that they frequently contain milky juice. They are found singly, or in little bundles, near to, or in the place of, the liber-bundles ; and are sometimes branched, ex. gr.y in Iloya camosa (according to Meyen), and very beautiful in Sar-costemma viminale. The configuration of their walls is entirely the same as in old milk-vessels.

The Milk-vessels, in relation to their origin, have been at present but little examined. They appear at first as enlarged intercellular passages,

and without any visible membrane (fig. 65.) to form them. Nor does any membrane appear to exist over the furrow formed by two neighbouring cells, as it does in all true cells. In old vessels, also, we often find impressions and projecting angles, showing that they must have fitted accurately into the surrounding cells (66. A, B). They are mostly branched in so compound a manner, that it is not often possible to examine a cell in its entire length (fig. 67.), yet it is easy to separate it into its parts if the tissue is treated with nitric acid. Without this means it is easily seen that they

€l Intermediate formation between liber-cells and milk-vessels from the bark of Cero-ptgia dichotomy The spiral stripes are drawn only in one half.

a Milk-vessels from the leaves of LimnocAaris HumMdtu The walls of the upper part of the vessel at a are fallen together. The arrows show the direction of the cur* rents. Every milk-vessel is enclosed by two rows of smaller and longer cells of parenchyma.

• Ueber Circulation des Saftes im Schöllkraut. Berlin, 1821. Natur der lebenden Pflanze. Berlin, 1832.

m A, A transverse section of a thickened milk-vessel from the bark of the stem of Euphorbia c<zrvlttcen$y with the walls of the same lying upon the cells. B, A longitudinal section of the same, isolated through maceration. The sides of the vessel aie irregular, from being pressed into the surrounding cells.

m Longitudinal section from the rind of Euphorbia trígona, parallel to the medullary rays. Many of the vessels branch and anastomose» whilst others end in blind extremities. Irregularly formed starch granules are seen in their interior.

extend through the entire length of a plant, and often end in a cul de sac. This is so obvious in some forms of leafless Euphorbiacece, that it is wonderful how any difference of opinion could have existed on the point. In the older vessels, also seen well in the leafless Euphorbiacete, the spiral bands and the deposit-layers on the walls are easily distinguished, so that the lateral development of these organs agrees entirely with that of cells.

In their relation to one another, these three forms of tissue, as well as the receptacles of milk without proper walls, seem mutually to represent each other. They are seen before the vascular bundles of the stem, as receptacles of milk in Mammillaria, as liber in Cereus, as transitionary forms in the Apocynacea and Asclepiadacecey which in some species resemble liber-cells, whilst in others, as in Sarcostemma viminale> they are not to be distinguished from milk-vessels.

History and Criticism. — The liber and the milk vessels were known to the earliest observers. The proper walls of the last were first seen by Mirbel, but more accurately observed by Schultz, whose observations, overloaded by false theory and hasty inferences, have led to this principal result, that a large proportion of the milk-vessels do really possess a peculiar covering.* His theory of their origin, founded on insufficient observation, has become now quite antiquated. Unger tj3l klay7-cxü.

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vsi, I I "j iiu iiM AL Tissi'K (Trlu €j)idermoidea\ is univer-!•«ill\ lli« in-ill rxirnistl hiytM1 nf ivIIh of a plant, so far as they can Im iIi«*i iiii* iiinln 11 11 «»in tin* evil* tliry cover, by their form and con* I t ui.« "i'hr\ nnly r\ii| 11! Ilir higher Cryptogamic and in nearly all

.i /Vim /■/"!./.# »im, ii <<iittimioiis layer of cclls, which may be •is-.mi ilmilrii iiiIh I In it kinds, according to the medium in which

I /'/ tttu tunn, l,,.\iTi,diii«i1lv dclicate, homogeneous, transparent t •11-, Kill. «1 wiih riili»uilr.-.t jtiiccs, and covering the surface without h>i nihil* 1111«'iI'l'lliiLir pa* ¡ly.rn. It is always present in the growing l«.ui i nl % mul \rinaiu.*« longest in closed cavities, as in the • MiiM, but rh injTi in«« -Ily into one or other of the following Im Ill'« .

• / . i on m ■ i Hi1." ft compact I Is flattened outwards, though not .si to t .mil wohtMii iuuiwllulur |K\ssages owning cxter-u.ilU I lu \ As \i li»iv«l \u iho wator aiul in the earth.

i r i ■ , li of \orv tlat tabular c^lls, whose w .\W> I n% i.tili .nut w\\U .iiv usually compact. They are ■ » ii%iiII\ plutvl \ iv» o.u'h otlu-r; but in most plants there

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1. .1 section parallel exists, at particular points, an intercellular passage, which, through the other intercellular passages and spaces, enables the subjacent parenchyma to communicate freely with the external air. At the inner opening of these intercellular passages, are placed (except in Salvinia and Marchantia) two semi-lunar parenchyma-cells, with their concave edges turned towards each other, which, according to the amount of their turgescence, allow a greater or less space to exist between them, or close the intercellular passage up altogether. These two cells, with the intercellular openings, are called stomates (stoma).
2. Appendicular Organs. They are all found upon the surface of plants, and are formed from cells. They are:
3. Papilla, which are mere extensions of the external cell-wall, in the form of little elevations, as upon the petals of flowers; or as vesicles, as in Mesembryanthemum crystallinum; or as apparent hairs, as the so-called root-hairs.
4. Hairs (Pili) consist of one or more thin-walled cells, varied in their form and arrangement, and planted upon the epidermis. They are simple (pili simplices), branched (p. ramosi), stellate (p. stellati), scales (lepides), knobbed (jp. capitati), glandular (p.glandu-liferi) if the upper cells secrete a peculiar fluid.
5. Seta, stiff*, thick-wailed, pricking cells.
6. Stings (Pili urentes) are stiff, thick-walled cells, terminating either in a point or a little head turned on one side, and mostly containing an irritating secretion. The cells at the base are often thin-walled, club-shaped, and swollen, and the whole enclosed by a number of wartlike cells produced from the epidermis.
7. Thorns (Aculei) consist of numerous rigid, thick-walled cells, firmly bound together, and terminating in a sharp point.
8. Warts ( Verruca), formed out of many compact semicircular and variously formed cells.
9. Cork (Suber). In the cells of the epidermis there is often collected a grumous substance, from which are developed flat tabular cells. The epidermis bursts, and thus is formed what is popularly called " bark," or, where it is strongly developed and elastic, " cork," as in juicy fruits, but especially in the second year's stems of the Qnercus Suber.
10. Root Sheath ( Velamen radicum). In most tropical Orchi-dea, and some Aroidea, there exists upon the epidermis of the roots (the adventitious roots) a layer which is ordinarily composed of the most delicate cellular tissue, whose contents are entirely air.

The controversy about the nature of the epidermis was only possible at a time when the conception of the elementary structure of plants was of a very imperfect kind, and a false analogy with the epidermis of animals led to erroneous conclusions.

When a part is about to be formed from the cambium in phanerogamic plants, the first thing that meets our view is a layer of one or more series of delicate cells, which are homogeneous and contain a clear fluid, r 3

and which form the external boundary and cover over the developing part. These cells of various signification I call Epithelium (fig. 69. a). Hie same thing may be observed in the so-called vascular cryptogamic plants (Ferns, Lycopodiacece> Equisetacece, Rhizocarpece). It is also seen in the Marchantiacece. This epithelium differs according to the external influences which act upon it. It is 71 only in a few cases that the epithelium retains its true character for any length of time, as in the cavities of the ovary. In the air, in water, or in the earth, it becomes changed more or less, the cells become more compact, and their external surface flattened (fig. 70. a) in the air, so that most epidermis-cells have a tabular or ligulate form (fig. 71. a). The forms which these tissues assume are very numerous. In the more delicate forms of these external coverings, as seen in the petals of some plants, individual cells elevate themselves above the surface (fig. 72. a), and thus form a transition to the simple forms of hairs.

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