The Ycast-plant — Fermentation. 83 



yeast-plant, and that the cessation of fermentation in the ordinary 

 course of natural operations is the result of the consumption of 

 the available nitrosjenous ingredients of the fermenting liquids. 

 If we remove a small portion of yeast from a fermenting wort, wash 

 it and place it in a solution of -pure mrjar, it will grow but for a 

 little time, until its own nitrogenous matter is consumed in the 

 •'waste" which takes place in cell-division. The new cells 

 dwindle in size and their growth is soon arrested. By supplying 

 nitrogen, on the other hand, the growth may be kept up until all 

 the sugar disappears. 



During the growth of the yeast-fungus, it is this nitrogenous 

 formative substance in the interior which carries on the processes 

 of nutrition and growth ; as it elaborates the food imbibed in a 

 liquid form through the cell-membranes, it increases in bulk and 

 pushes out the wall into buds, supplies them with their propor- 

 tion of " protoplasm," and throws them off. It is found, more- 

 over, that the protoplasm gradually passes entirely into the 

 progeny of bud-cells, and the old parent cells are left as empty 

 collapsed sacs. 



There is no reason to question the propriety of extending our 

 conclusions from the yeast-fungus to all other plants of that class 

 which live in essentially analogous conditions. And the con- 

 struction and character of the substance of Fungi, thus fed upon 

 organic matter, is quite in harmony with the gross, watery, and 

 perishable substance which is produced by the growth of the 

 higher plants when over-fed with nitrogenous manures, and at 

 the same time limited in their supply of light and air. VVe may 

 further extend the same set of conclusions to the early growth 

 of shoots from germinating seeds and tubers (like tlie potato), 

 where the protoplasmic substances at tlie growing points, when 

 stimulated by heat and moisture, commence and carry on the 

 cell-developinent without the aid of light, and produce from the 

 store of organic food laid up in the old tissue, soft succulent 

 growths, and continue to develop in tlie same way if supplied 

 with nitrogenous food and abstraited from the influence of light. 

 The remarks contained in the foregoing paragraphs afford an 

 explanation of the un(h)ubted fact that plants cannot grow without 

 a supply of nitrogen in some f(jrin or otfier, and that increased 

 supplies of nitrogenous matter a<t upon vegetation as a stimulus ; 

 for we have seen that the vital part of the structure is not the more 

 solid and permanent cellular substance of the ternary compounds 

 destitute of nitrogen, but the /'or nuUive substance contained in the 

 cellular chamljers, the jirofo/j/asni. 



In tliese inquiries, iiowever, we have left out of view the in- 

 fluence of the most important of the external agents concerned 

 in the development of plants, namely, light. VVc have noticed 



G 2 



