1073 



TISSUES, VEGETABLE. 



TISSUES, VEGETABLE. 



1074 



Fig. 2. 



(Atractenehyma), Sinuous (Colpenchyma), Branched (Cladenchyma), 

 Entangled (Dsedalenchyma), have been described by Morren. 



Prosenchyma differs from Parenchyma iu the cells always having 

 an elliptical form which taper to their extremities, where they overlie 

 each other. This form of tissue is found only in the bark and wood, 

 and is a transition from cellular to what is called 

 woody tissue. Meyen applies this term especially 

 to the tissue forming the wood of Conifera; and 

 Oycadace<e. In these families this tissue is 

 marked with dots, which are surrounded by a 

 circle (Jiff. 2). These dots were formerly sup- 

 posed to be glands, and to secrete the resinous 

 matter which abounds in them, and hence it 

 was called 'glandular woody tissue.' The re- 

 searches of Mohl and others have however 

 shown that these dots are the result of the de- 

 velopment of fibre within the walls of the cells, 

 and in tlds view the Prosenchyma not only constitutes a transition 

 from cellular to vascular tissue, but also a transition from fibro- 

 cellular to fibre-vascular tissue. 



It is mostly iu the interior of the cells of cellular tissue that those 

 crystalline bodies called Raphides are found. They occur singly or in 

 bundles, and have au aeicular form, and are long or short according 

 to circumstances. In length they measure from l-40th to l-1000th part 

 of an inch. These crystals were first observed in the proper juices of 

 plants, and have been subsequently found in all parts of plants where 

 cellular tissue exists. They were formerly supposed to exist between 

 the cells, but later observers have seen them in cells, and they pro- 

 bably exist in both situations. The form of these bodies is not 

 satisfactorily determined. Mohl describes them as right-angled four- 

 sided prisms vanishing into points. Quekett, who is one of the latest 

 observers on this point, says they are decidedly four-aided prisms, but 

 not always right-angled. Those which are conglomerated are called 

 crystal-glands (krystal-driisen) by Meyen. They seldom present more 

 than the pyramid of each little crystal composing them. The propor- 

 tion in which they exist in plants is sometimes very great. In some 

 species of Caclacece, according to Quekett, the crystals equal the 

 weight of the dried tissue. One hundred grains of Turkey rhubarb- 

 root yield between 30 and 40 grains of Haphides ; the name quantity 

 of tissue of Scilla maritima yielded 10 grains. In most plants these 

 crystals are composed of either oxalate or phosphate of lime, llaspail 

 says the crystals of the oxalate of lime are four-sided prisms with 

 pyramids of the same base ; those of the phosphate, six-sided prisms. 

 In C'/iara crystals of carbonate of lime occur in great abundance on 

 the outside of the tissue, and we have observed them in the inter- 

 cellular passages immediately under the epidermis, but they do not 

 occur in the interior parts of the plant. Schiibler found that the 

 crystal-glands of Hydruriu cryttallophorut consisted of carbonate of 

 lime, and Saigey and De la Fosse found silica in the crystals of the 

 Mirabilii Jalapa. Silica is a very prominent constituent of the 

 GramiiuKece, but is seldom found crystallised. It gives the hardness 

 to the epidermis of the Dutch Rush, and is secreted in large quanti- 

 ties in the joints of the stem of the Bamboo, and is used as an article 

 of commerce under the name of Tabasheer. From the variable form 

 of the crystals in plants it may be inferred that other salts form them 

 besides the above. These bodies do not appear to be necessary parts 

 of the tissues in which they occur, and they have been compared by 

 Link to Calculi and other concretions iu the animal kingdom. This 

 view is rendered very probable by the fact that they are always com- 

 posed of those elements which the plants take up from the soil as 

 necessary nutriment Meyeu has pointed out the fact that plants 

 growing near the sea will throw off the superabundance of chloride 

 of sodium in their tissues in the form of crystals ; and we have found 

 crystals of carbonate of lime most abundant iu Chara flexilis, where 

 the water in which it grew contained most of that substance. Phos- 

 phate of lime is necessary to the nutrition of many plants, and the 

 elements of oxalic acid exist iu the sap of all plants ; and when these 

 are in greater abundance than the vital energies of the plant can 

 appropriate, the laws of chemical affinity come into play, and crystal- 

 lisation is the result. 



The Intercellular System. The walla of the loose spheroidal cells 

 in Merencbyma consist of a single membrane, but the walls of the 

 more closely-pressed cells of Parenchyma consist of two membranes, 

 originally distinct, but fused into one by growth. It frequently 

 happens that the walls of the cells are not accurately applied to each 

 other, and consequently spaces of various kinds occur between the 

 cells. These ore culled Intercellular Passages. They occur in the 

 greatest abundance in the loose Merenchymatous Tissue. When these 

 passage-; e-ist between the walls of two cells whose sides are united 

 in their middle and recede towards their margins, they are called by 

 Link Meatus Intercellulares. These are most frequently met with 

 in the epidermis of plants. Where the passages are formed of three 

 or more cells the fides of whose walls do not touch, they are called 



yjuctus Intercellulares. These are very well seen iu the parenchyma 

 if the stem of the Iris and Hyacinth, and Heraclcum. These pas- 

 ages have been supposed by De Candolle and others to convey the 

 ap ; but this has probably arisen from an error in observation, as 

 hey are easily filled with nap when cut through. 

 HAT. HIST. DIV. VOL. IV. 



Another kind of Intercellular Formation are the Air Cells (the 

 Lacuna; Intercellulares of Link), which are large cavities formed iu 

 the tissue of plants, and whose walls are entirely formed of cellular 

 tissue. They may be very distinctly divided into two kinds, the 

 regular and the irregular. The regular exist under the epidermis 

 of many plants, and vary in size, but have in all cases a regularity of 

 structure, their sides being formed of equal-sized cells of cellular 

 tissue. They may be seen in the leaf-stalk of Calla sEthiopica, the 

 stem of (Enanthe PhellandHum, and the petioles of Nymphaza. They 

 are very common in water-plants. They are always filled with air in 

 these plants, and serve as a means of buoying them up in the water. 

 The irregular air-cells (Lacunae of Link), are found in old plants; 

 they arise from the growth of the plant tearing asunder the cellular 

 tissue, or from a deficient development or even the absorption of this 

 tissue in particular directions. They may be seen in the stem of the 

 fronds of the Aspidium Filix Mas, of Uippuris, and quise!um, and 

 in nearly the whole of the family Umbelliferce. 



All plants are covered with a layer of external cells, which are 

 separated from the adjoining tissue and may be often peeled off in :i 

 layer. This is called Epidermis, and consists mostly of one row, but 

 sometimes of tws rows of cells, which are generally smaller and denser 

 than those of the surrounding tissues. It is in these cells that the 

 openings occur which are called Stomates. [STOMATES. ] 



Schleiden divides the epidermis into three forms, which he calls 

 Epithelium, Epibtema, and true Epidermis. The epithelium is that 

 form of epidermis which is continued into the interior of the organs 

 of plants, as in the inside of the fruit. Epiblsema is applied to that 

 modification of the tissue which is found on the surface of the leaves 

 and other parts of aquatic plants. The true epidermis is found on 

 the outside of the stem, branches, leaves, and other organs of plants. 



The epidermal cells are often elevated above the surface. When 

 three or four, or more, form a small projection, it is called a Papilla ; 

 when it is longer it is a Hair [HAllis] ; when it becomes harder it is 

 a Setum, and when hard and pointed a Prickle. Warts are still larger 

 excrescences of the epidermis. 



Fibro-Cellular Tissue, or Ineuchyma, consists of cells formed of 

 membrane, iu the inside of which fibre is developed. This tissue may 

 be divided into two kinds, genuine and spurious ; the genuine being 

 that in which the fibre is distinctly marked on the inside of the cell, 

 and the spurious that iu which the fibre, either by absorption or the 

 union of its various parts, forms rings, bars, dots, and other appear- 

 ances on the sides of the cell. The genuine fibre-cellular tissue is 

 mostly found in parenchymatous and proaenchymatous cella. It has 

 been known for a long time amongst botanists, and was first described 

 by Hedwig, who was followed by Moldenhavver and others. It is 

 abundant in the external parchment-like layers of the aerial roots of 

 Orchidacete, and has been described in Oncidium, alti&simutn, Aero- 

 pera Loddigesii, Bras&avola cordata, &c. It occurs in the hairs of the 

 pericarp of many of the Composite, as in Pei'dicium taraxaci, Senecio 

 Jlaccidus, and Trie/iodine humilis. Horkel has described it in the 

 epidermis of many Labiate?, as Zizlphora, Ocymum, and many Salviw. 

 The seed-coats of many plants possess it, as Gilia Ipomopsis, Pule 

 Mijniu.ni Cantua, and Caldaria; and Kippist has demonstrated its 

 presence in many of the species of Acanthacea;. In some of these 

 cases, and many others might be mentioned, the fibre appears to con- 

 stitute the whole of the cell, and this has led to the supposition that 

 it is found independent of the cell-wall or cell-contents. 



The fibre in these cells varies in its position and form. Iu the cella 

 of the leaf of Oncidium altissimuni they are very distinct, and occa- 

 sionally branched. In the testa of the seed of Maurandya Barcleyana, 

 where they were first pointed out by Lindley, the fibres run in different 

 directions over each other, forming a network. In the endotheciuiu 

 of Calla jEthiopiaca they are parallel, and in this form are very com- 

 mon in the same organ of other plants. In the endothecium of Nym- 

 pluxa alia the fibres form regular arches arising from a plane base. Iu 

 the elaters of Junyermatmia and in the testa of Acantltodiumthe cells 

 are greatly elongated, with a single spiral fibre in their interior. 



The spurious fibro-cellular tissue includes the Porous and Dotted 

 Cells of many authors, the CelluUc Porosso et Punctate of Link. If 

 a portion of the parenchyma of Viscum album be examined, the insido 

 of the cells will be found to possess a number of bright spots. They 

 were first discovered by Treviranus in Cycas revoluta, and supposed 

 by him to be granules. They were thought by other observers to b 

 pores; hence their name Porous Cells. These spots however are nob 

 pores, but depressions, produced by the breaking up of the spiral 

 deposits iu the interior of the cell. 



A transition from porous cells to porous tubes is seen iu the tissue 

 which has been called Bothrenchyuia. In this tissue, which can be 

 well seen in Pliytocrenc, as well as Cycas, a number of truncated 

 porous cells are placed one on the other so as to form a cylinder, 

 which becomes a tube by the absorption or removal of the cellular 

 partitions. Porous vascular tissue is referred to this form by Lindley 

 under the name of Continuous Bothrenchyuia, as the partitions or 

 iniou of the cells are not visible. Where the points of union of the 

 cells are evident, he calls it Articulated Bothrenchyma. 



Dotted Cells have their walls marked with dark spots. These cells 

 have been observed in the pith of Calycanthus fliridta and iu the stem 

 of Dracana terminalii. They appear only to differ from the porous 



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