x DEVELOPMENT OF THE TEXTURES. 



account of the development of the tissues of vegetables ; for it was in conse- 

 quence of the discoveries made in the vegetable kingdom that the happy 

 idea arose of applying the principle of cell-development to explain the 

 formation of animal structures, and they still afford important aid in the 

 study of that, as yet, more obscure process. 



OUTLINE OF THE FORMATION OP VEGETABLE STRUCTURE. 



When a thin slice from the succulent part of a plant is viewed under the 

 microscope, it is seen to consist chiefly or entirely of a multitude of vesicles 

 adhering together, of a rounded or angular form, and containing various 



coloured or colourless matters in their 



Fig. i. interior ; these are the elementary 



cells (fig. i. ; fig. ir., 12 ). These cells 

 are so constructed that their walls are 

 in close apposition, or are separated 

 only by an intercellular substance, 

 which, according to Hugo von Mohl,* 

 has so great a similarity to the sub- 

 stance of the cell- walls that it is often 

 impossible, even with the aid of chemical 

 re-agents, to discover a line of demar- 

 cation between them. That eminent 

 Fig. I. NUCLEATED CELLS PROM A phytologist supposes that within what 

 BULBOUS ROOT ; MAGNIFIED 290 DIA- is commonly called the cell- wall there 

 METERS (Schwann). exists an extremely delicate mem- 



brane, constituting an interior vesicle, 



which he names the " Primordial utricle." This is in most cases so closely 

 applied to the exterior wall as to be undistinguishable ; but in young cells, 

 and in those of strictly cellular plants, such as the Algse, <fec., during the 

 whole of their existence it may, according to Mohl, be separated by treating 

 the tissue with alcohol, or hydrochloric or nitric acid, and then the interior 

 vesicle appears shrivelled up and separated from the wall of the cavity. 

 But the reality of the alleged primordial utricle has been called in question, 

 and the supposed internal membrane is held to be merely the limiting sur- 

 face of the cell-contents shrunk away from the inside of the containing 

 cavity, and perhaps somewhat consolidated and defined by the re-agents 

 employed. Still, whether the cell-contents have a vesicular limiting mem- 

 brane or not, they originally present a marked contrast in chemical nature 

 to the containing cell-wall and intercellular substance, and would appear to 

 fulfil a different purpose in the process of tissue-development, f 



Besides such cells, phsenogamous or flowering plants contain tubes, 

 vessels, and other forms of tissue (fig. u., 4 6 ) ; but a great many plants of 

 the class cryptogamia are composed entirely of cells, variously modified, it 

 is true, to suit their several destinations, but fundamentally the same 

 throughout ; nay, there are certain very simple modes of vegetable existence, 

 in which a single cell may constitute an entire plant, as in the well-known 

 green powdery crust which coats over the trunks of trees, damp walls, and 



* Die vegetabilische Zelle ; or English translation by Henfrey. 



+ See an interesting discussion of this subject by Mr. Huxley in the British and 

 Foreign Medical Review for 1853. 



