THE TREES OF AMEEIOA. 37 



same law, the principle of dell formation. Starting, then, with the idea that all 

 vegetable forms, from the mushroom to the tree, are but a heaping up as it were 

 of little cells, like a pile of soap bubbles, or like the forms wrought in embroid- 

 ery, which, when examined minutely, are found to consist of a series of similar 

 stitches, which, when combined, produce such various results, we shall be pre* 

 pared to examine to some extent into the growth of plants ; that is, into cell- 

 life, which, according to Professor Schleiden, is " almost the Only really scientific 

 part of botany." 



The basis, then, of the structure of all the multiform developments of vegeta- 

 ble life, is a little vesicle composed of a membrane, like, so to speak, the skin of 

 water which is, stretched around a portion of air, and is called a bubble. This 

 cell, which, it must be recollected, is so small as to require a microscope in order 

 to examine it, is usually transparent and colorless. Within the outer membrane, 

 which is somewhat firm in structure, is found a soft, yellowish substance lining 

 the first, and thus constituting one of the coats of the cell. The external or 

 proper cell-wall is composed of carbon, hydrogen, and oxygen ; the internal lin- 

 ing membrane has, in addition to these, nitrogen. Out of this internal lining, 

 or primordial utricle, as it is called, spring the new cells, which become crowded 

 together in the process of growth, and constitute the cellular tissue which forms 

 the whole structure of the plant. We may regard the cell as a sort of independ- 

 ent existence, living by its own inherent power. It draws its nutriment from 

 sources in contact with it, and, by chemical processes which are continually going 

 on within it, changes this into its own proper tissue, thus producing growth, and 

 also into substances, some of which are stored up for future uses, and others ex- 

 pelled as unsuited for its special purposes ; but still, in accordance with the univer- 

 sal law which makes every thing useful, these excretions have their place in the 

 economy of nature. Thus the life of the cell, and also of the whole plant, since 

 it is but an accumulation of cells, consists in this constant change of absorption 

 and nutrition, the formation and decomposition of substances. In the growth 

 of plants the cells undergo changes in form as they are subjected to the laws of 

 growth ; that is, some become changed by simple enlargement, others are elon- 

 gated, flattened, or become star-like in shape ; some are spindle-shaped, others 

 are stretched out into the form of long, thin filaments. Cells are, however, subject 



