4 BOTANY. • 



* 

 /Soda, Lime, Alumina, Magnesia, Silica, and Iron ; more rarely Iodine, 

 Chlorine, Copper, Bromine, and Manganese. These will be subsequently 

 referred to more at length. Starch is included in the cells of all plants at 

 some period of their existence, and forms one of the most important distinc- 

 tive characters between the animal and vegetable tissues. Crystals also, or 

 llaphides of various shapes and characters are found in the interior of cells, 

 either lying loose or suspended from the walls. Sometimes there Avill be a 

 single large crystal in a cell, and again several may be inclosed together. 

 They abound in certain plants, as Cacti, to such an extent, as to exceed in 

 weight the other constituents of the tissue. The raphides are all formed by 

 the action of organic acids, as phosphoric, oxalic, (fcc. 



Jelly is another occasional element of cells. This is hard and horny 

 when dry, slowly soluble in water, and unacted on by iodine. It sometimes 

 fills particular cells, as in the stems of some Cacti. It is to this substance 

 that carrageen moss and other plants owe their gelatinous properties. 

 Chlorophylle, the green coloring matter of plants, and Chromule, the 

 coloring matter not green, are additional contents of cells. 



Various and quite conflicting opinions have been propounded by different 

 eminent vegetable physiologists as to the development {Cytogenesis) and 

 functions of cells. Perhaps the more generally received opinion is, that in 

 the blastema, or primordial matter, the nucleus, which is itself a minute cell, 

 is fii'st formed, and exerting a directing influence upon the inclosing matter, 

 causes it to assume a cell-shape. With the absorption of new matter from 

 the blastema the nucleoli increase in size and finally separate, each one 

 forming around itself new cells, which, enlarging, burst the oiiginal cell. 

 The new cells contain nucleated nuclei, by means of which the same 

 operation is repeated, the increase taking place in a determinate direction. 

 This constitutes the endogeuous theory of cell development. . The exogenous 

 theory supposes an influence to be exerted by a cell on the surrounding 

 matter, resulting in the addition or afj^reiiation of new matter. This view 

 does not require the existence of a nucleus. According to others, again, the 

 old cell becomes separated by a constriction, or a projecting partition, into 

 two cells, each of which may or may not include a nucleus. This is the 

 merismatic or fissiparous theory. Many attribute to electric currents, 

 produced by the various chemical actions, the influences which cause the 

 different cell phenomena. The development of cells sometimes takes place 

 with extraordinary rapidity, especially in the Fungi. Thus, in Bovista 

 gigantea, they have been supposed to be produced at the rate of sixty-six 

 millions in a minute. 



2. Vascular Tissue. 



Vascular Tissue, or Angienchyma, consists of tubes whose length 

 greatly exceeds their breadth. They may be formed of membrane only, 

 or of membrane variously modified. Woody fibre, or ligneous tissue 

 {Pleurenchyma), consists of tubes or elongated cells, of a fusiform or 

 spindle- shape, with the walls greatly thickened by sclerogenous deposits. 

 4 



