PHYSIOLOGY. 253 



starch. In several parts of the Plant, but more especially 

 in the leaves, and flowers, there resides the substance which 

 gives them their peculiar colors. This is in the form of 

 minute globules, and has been named by Decandolle, 

 Chromule. 



The cells of the ligneous, or woody portion of trees and 

 shrubs, are incrusted with particles of a more dense mate- 

 rial, peculiar to vegetable organization and termed lignin. 

 It is this substance which principally contributes to the 

 density, and mechanical strength of what are called woody 

 fibres. This part consists of collections of fusiform, or ta- 

 pering vessels, hereafter to be described, and which interlace 

 each other, so as to form cohering bundles, which resist me- 

 chanical forces much more effectually than they would do, if 

 they were laid in a longitudinal direction with respect to 

 each other. 



CELLULAR PLANTS. The cellular structure above de- 

 scribed, is confined chiefly, but not entirely, to the Crypto- 

 gamous, and Monocotyledonous class of Plants. These 

 Plants, as we have shown, when treating of " Natural Bota- 

 ny," increase by the accumulation of matter in their inte- 

 rior parts, and are called Endogenous Plants. This struc- 

 ture is apparent, even to the naked eye, in the Indian Corn, 

 Lily, Iris, and many other similar Plants, the stalks ot 

 which being cut lengthwise show the cells, or the cellular 

 tissue. 



The cellular structure is the most obvious physiological 

 character of the Acotyledonous, or Cryptogamous class of 

 vegetables. 



The Monocotyledonous species, are the first remove from 

 the Acotyledonous, and hold an intermediate rank between 

 them and the Dicotyledonous Plants, in which vegetation 

 acquires its highest form of development. 



In the Cryptogamia, or Cellulares, the plants are formed 

 entirely of the cellular tissue, as shown by Fig. 222, without 

 woody fibre, or spiral vessels. Fig. 224 rep- Fi - 224 - 



resents a transverse section of a stem belong- 

 ing to this division. It is composed of cells 

 and membranes alone. Examples of this 

 structure are presented by the Mushrooms 

 and Sea-weeds. 



COTYLEDONOUS, OR VASCULAR PLANTS. By Vascular 



Plants, is meant those containing spiral vessels, as a part of 

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