VEGETABLE GROWTH. 171 



tion of plants, are transformed one into the other or into 

 cellulose, according to the requirements of the vegetable 

 economy. Only a small portion, however, of the water 

 taken up by the roots is assimilated, much the largest part 

 being exhaled by the leaves. It performs, nevertheless, 

 most valuable service as a common carrier throughout the 

 various parts of plants, both of those nitrogenous and 

 other substances absorbed in very dilute solution from the 

 soil, and of those organic compounds formed within the 

 plant, and essential to its growth in the several stages of 

 its development. 



The vital fluid, corresponding to the blood of animals, and 

 existing in every young and growing vegetable cell, is called 

 protoplasm, and is a somewhat viscid substance, containing, 

 in addition to carbon, oxygen and hydrogen, nitrogen, sul- 

 phur and phosphorus. Other similar substances are laid up 

 in the seed in a more concentrated and permanent form for 

 the sustenance of the young seedling at the period of germi- 

 nation. As the herbiverous animals can derive their nitro- 

 gen, sulphur and phosphorus from no other source than these 

 so-called albuminoids of plants, and as ripe seeds can rarely 

 be obtained in sufficient quantity for their exclusive support, 

 it is interesting to observe that they are generally formed for 

 the consumption of large quantities of tender herbage, which 

 is easily digestible, and contains these essential elements of 

 their nutrition in a <^^ery dilute form in the protoplasm of the 

 growing cells. 



Vegetable growth is an increase in size and weight in con- 

 sequence of the multiplication and enlargement of cells, and 

 occurs chiefly in the vicinity of the cambium layer which, in 

 the growing season, envelopes every living root, stem and 

 .branch, and penetrates between the two layers of every leaf. 

 The mode of cell development has been carefully studied with 

 the aid of the microscope, and may be best observed in aquatic 

 plants with large cells, or in transparent hairs, such as are 

 often found on the leaves or flowers of plants in dry situa- 

 tions. • 



The protoplasm in aquatic cellular plants is usually thin 

 and colorless, and encloses a minute globule called a nucleus, 

 which often contains still more minute nucleoli, together with 



