T I S 



503 



X I S 



is necessary to the nutrition of many plants, and the ele- 

 ments of oxalic acid exist in the sap of all plants; and 

 when these are in greater abundance than the vital ener- 

 gies of the plant can appropriate, the laws of chemical 

 affinity come into play, and crystallization is the result. 



Growth, Form, $c. The vesicles, of cellular tissue are 

 very small, and cannot lie distinguished with the naked eye ; 

 and in fact all investigations on the structure, development, 

 and functions of the tissues of plants, can only be con- 

 ducted with the aid of the microscope. The measure- 

 ments of the cells give them a size varying from 3 yh to 

 ?' le TjW 1 f an inch in diameter. In the lower tribes, as 

 in the Fungi, their generation is very rapid, and it is well 

 known that mushrooms, puffballs, &c. will attain a 

 groat size in the course of .a single night. The force too 

 with which they are generated is very great, and there are 

 many well-authenticated instances of" agarics springing 

 up beneath pavements and displacing stones of great 

 weight and size. 



The walls of the loose spheroidal cells in merenchyma 

 consist of a single membrane, but the walls of the more 

 closely-pressed cells of parenchyma consist of two mem- 

 branes, 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 

 are called intercellular passages. They occur in the 

 greatest abundance in the loose merenchymatous tissue. 

 When these passages exist between the walls of two cells 

 whose sides are united in their middle and recede towards 

 their margins, they are called by Link meatus intercel- 

 lulares. These are most frequently met with in the epider- 

 mis of piants. Where the passages are formed of three or 

 more cells the sides of whose walls do not touch, they are 

 called (Indus intercellulures. These are very well seen in 

 the parenchyma of the stem of the iris and hyacinth, and 

 Heracleum. These passages have been supposed by De 

 Candolle and others to convey the sap ; but this has pro- 

 bably arisen from an error in observation, as they are easily 

 iilled with sap when cut through. Others again confound 

 these passages with the peculiar vascular tissue described 

 by Schultes as Laticiferous tissue (Cinenchyma). 



Another kind of intercellular formation are the air-cells, 

 the lucunif nitfrcMulares of Link, which are large cavi- 

 1 ie.s formed in the tissue of plants, and whose walls are 

 entirely formed of cellular tissue. They may be very dis- 

 tinctly divided into two kinds, the regular and the irregu- 

 lar. The regular exist under the epidermis of many plants 

 and vary in size, but have in all cases a regularity of struc- 

 ture, their sides being formed of equal-sized cells of cellu- 

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

 sethiopica, the stem of CEnanthe Phellandrium, and the 

 petioles of Nymphaea. 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, lacuncs of Link, are found in old 

 plants ; they arise from the growth of the plant tearing 

 asunder the cellular tissue, or from a deficient develop- 

 ment or even the absorption of this tissue in particular 

 directions. They may be seen in the stem of the fronds 

 of the Aspidium Fihx Mas, of Hippuris and Equisetum, 

 and in nearly the whole of the family Umbelliferae. 



The other organs which are formed by and found in the 

 midst of the cellular tissue are the sap-cells and gland*. 

 The sap-cells, the opangia of Link, consist of enlarged 

 cells of tissue, varying much in size, but always filled with 

 elaborated sap. They are found in the skin of the fruit of 

 the citron, pomegranate, &c. These are regular in form, 

 but in the roots and rhizomata of such plants as the ginger, 

 Archangelica, and Aristolochia, they are found of an irre- 

 gular form. The glands, which are by some supposed to 

 be the agents by which the peculiar secretions of the plant 

 immediately separated from the latex, are composed 

 iU pressed together, and assuming a variety of forms. 

 When examined, these cells are found to contain in many 

 iii^Hm-cr, the ri-sin, sum, oil, &c. which give to the plant 

 some of its peculiar physical properties. 



The organs just enumerated as present in the cellular 

 tissue are met with chiefly in the merenchymatous and 

 parenchynintotis forms. 



Vascular or Tabular Tissue consists of continuous I 

 of simple membrane, and comprehends the woody and the 

 laticifercus tissues. On the one hand they are distinguished 



by their length from the forms of cellular tissue, and on 

 the other hand by their plane membrane from those tissues 

 of which fibre forms a constituent element. 



Pleurenchyma,ot Woody Tissue (vasajibrosa of Link, ana 

 Fasergefasse, German), is found abundantly in the wood, 

 and especially the liber, of all plants. It is composed of 

 very long, thin, tough, transparent, membranous tubes. 

 No bars or dots are seen in their walls, although when 

 they cross each other the points at which they touch may 

 be taken for such markings. They taper acutely to each 

 end, and do not appear to have any communication one 

 with the other, although they arc occasionally seen with 

 open extremities, which Slack supposes to arise from the 

 breaking off of one fibre where it was united to another. 

 In the wood and bark of dicotyledonous plants they are 

 frequently mixed with prosenchyma, and in monocotyle- 

 donous plants with parenchyma. They grow by increasing 

 in length both above and below. Their diameter varies 

 from T^J to 3^55 of an inch. The walls increase in thickness 

 by the deposition of vegetable jelly, called by Turpin 

 sclerogen, to their insides, and in the woody tissue of 

 Betula alba and other trees the sclerogen may be seen 

 forming successive layers around the sides of tho tubes. 

 Their form is mostly cylindrical, but in Cycas revoluta 

 Link has observed them assuming a prismatic form. 



The tubes of woody tissue are very tough, and will resist 

 considerable force without breaking. It is on this account 

 that they are used extensively in the manufacture of cloths 

 of various kinds. The plants used most commonly for this 

 purpose are the hemp and flax. The fibres of Tilia, Daphne, 

 Lagetta, and of many of the plants of the order of Mal- 

 vaceae, are used for making mats, cordage, whips, &c. The 

 following is a comparative statement of the relative strength 

 of silk and some woody fibre : 



Silk supported a weight equal to 34 

 New Zealand Flax 23J 



Hemp ..... 10J 



Flax llj 



Pita Flax (Agave Americana) . 7 

 Woody tissue gives firmness and tenacity to the plant, 

 and assists in conveying the sap from the roots to the 

 leaves. 



Cinenchyma, or Laticiferous Tissue, consists of tubes 

 which are mostly branched and anastomosing ; their walls 

 are exceedingly delicate in young plants, and thicker in 

 old ones ; and they are characterised by conveying a fluid 

 called the latex, which differs from the sap in other parts 

 of the plant. [SAP.] The older botanists, Spigelius, Mal- 

 pighi, and Grew described them, but they were generally 

 confounded with woody tissue, till they were very fully 

 investigated by Schultes. In older writers they are called 

 vasa propria or peculiar ia ; by Link, v asa opophora. Some 

 writers have supposed that they are nothing more than 

 intercellular passages, and have denied that they po- 

 membranous parietes ; but their existence has been ascer- 

 tained, and the observations of Schultes on their structure 

 confirmed by Link, Meyen, Mohl, and others. The walls 

 of these vessels are mostly plain, but have been sometimes 

 observed marked with bars and fibres. They do not exist 

 in all plant*, and have not been found at all in the lower 

 forms of Cryptogamia, nor in some of the Phanerogamous 

 plants, as Valisneria and Stratiotes. Their most frequent 

 position is on the sides of spiral vessels, or amongst the 

 bundles of this tissue found in the midrib and nerves of 

 leaves. They are most obvious in the order Euphorbiaceee, 

 where the latex is of a white colour. This juice is not 

 always coloured or opalescent, but is sometimes quite clear. 

 The tubes are not always regular in size. In some species, 

 as in Glycine Apios, they are irregularly contracted and 

 expanded ; in Papaver nudicaule they have a moniliform 

 appearance ; in Acer platanoides they are very regular. 

 In the stem they are generally simple, but in very young 

 plants and the younger parts of plants they are branched, 

 and anastomose. (Fig. 3.) Link has observed their termi- 

 nating in blind extremities. In their distribution they 

 gradually diminish in size, and have been traced into the 

 most delicate parts of plants, as the hairs. 



Schultes supposes that these vessels perform the same 

 functions in the plant as the arteries and veins in animals. 

 The fluid in them has a peculiar motion, which he calls 

 cyclosis. [SAP.] 



Fibro-ceitular Tissue, or Inenchyma, consists of cells 

 formed of membrane, in the inside of which fibre is de- 



