CELL-LIFE. 551 



between animal and vegetable organization when reduced to its lowest 

 terms. 



As long as a cell retains its active protoplasm, it is capable 

 of producing new cells and organized forms of assimilated matter, 

 like starch and chlorophyll, in its contents. This is the case, of 

 course, in all nascent tissues ; but it ceases to be so at various 

 periods in different, parts of the vegetable organization. In all 

 woody tissues, in all pitted and spiral-fibrous cells, it disappears 

 early, secondary deposits of the ligneous character being formed 

 apparently from the watery cell-sap. In herbaceous organs, such 

 as leaves, in the cells of the Cellular plants generally, in fact in all 

 the properly living structures, the protoplasm remains. 



This explains why the power to form adventitious buds exists not only 

 in the cambium-layer of the higher plants, but, under certain conditions, 

 even in the leaves (as in Bryophyllum, Gloxinia, &c.), and why gemma- 

 tion or propagation by little cellular bulbils, or isolated cells detached 

 from the vegetative organs, is so common among the Cellular plants, and 

 in the Mosses and Liverworts, where parenchymatous tissues so greatly 

 predominate. . 



Nutrition in Cellular Plants. 



The elementary structures being essentially alike throughout the 

 Vegetable Kingdom, and the physiological phenomena of vegeta- 

 tion depending almost entirely upon processes taking place in the 

 individual cells, it is very instructive to examine the phenomena of 

 nutrition and growth in those simply organized plants in which we 

 are able to observe directly the changes in the living cells. 



Many cellular aquatic plants are especially adapted for these researches, 

 from their simple structure, transparency, and their aquatic habit, which 

 permit us to keep them in a growing condition in glass cells beneath the 

 microscope. By way of illustration the history of the Yeast-plant is 

 subjoined. 



The Yeast-plant. What is called the "Yeast-plant" consists of a 

 particular form of the mycelium of a Fungus (fig. 587, Torula cere- 

 visice). It is composed of simple cells, which will go on multiplying 

 by budding for an indefinite time if placed in a liquid containing a mix- 

 ture of saccharine or dextrinous substances, together with albuminous 

 matters, at a moderately warm temperature (59-67 F.), bubbles of car- 

 bonic dioxide being given off. These cells are simple membranous vesi- 

 cles, with their walls formed of a modification of the compound (cellulose} 

 of which all vegetable cell-membranes are formed, and mixed with which 

 are very minute quantities of sulphur, phosphorus, potassium, magne- 

 sium, and calcium. Within the cells exist nitrogenous matter in the 

 condition of protoplasm, fatty matter, and water. The increase of the 

 plant is dependent on the assimilation of substance requisite for the pro- 

 duction of new cell-membranes, and of other substances to furnish new 



