VEGETABLE ORGANIZATION. 63 



through the membranes which form their sides, and not by 

 any apertures capable of being detected by the highest pow- 

 ers of the microscope. 



If all the cells consist of separate vesicles, as the con- 

 curring observations of modern botanists* appear to have 

 satisfactorily established, the partitions which separate them, 

 however thin and delicate, must consist of a double mem- 

 brane, formed by the adhesion of the coats of the two con- 

 tiguous vesicles. But as these coats can hardly be supposed 

 to adhere in every point, we may expect to find that spaces 

 have been left in various parts between them; and that com- 

 munications exist to a certain extent between all these spaces; 

 so as to compose what may be regarded as one large cavity. 

 These have been denominated the intercellular spaces; and 

 they have been supposed to perform, as will hereafter be 

 seen, an important part in the functions of Nutrition. 



Fluids of different kinds occupy both the cells and the 

 intercellular spaces. The contents of some is the simple 

 watery sap; that of others consists of peculiar liquids, the 

 products of vegetable secretion: and very frequently they 

 contain merely air. In many of the cells there are found 

 small opaque and detached particles of the substance termed 

 by chemists, Feciila, of which starch is the most common 

 example. In several parts, and more especially in the leaves, 

 and in the petals of flowers, the material which gives them 

 their peculiar colour is contained in the cells in the form of 

 minute globules. De Candolle has given it the name of 

 Chromule.\ 



The cells of the ligneous portion of trees and shrubs are 

 farther incrusted with particles of a more dense material, 

 peculiar to vegetable organization, and termed Ligniiie, It 

 is this substance which principally contributes to the den- 

 sity and mechanical strength of what are called tlie Woody 

 Fibres, which consist of collections of fasiform, or tapering 

 vessels, hereafter to be described, surrounded by assemblages 



* In particular, Treviramis, Kioscr, Link, Du I'etit ThoiKU-s, I'oUiiii, Ainlci^ 

 Dutrochet, and De Candolle. 

 f Organographie, Tom. 1, p. 19. 



