552 



PHYSIOLOGY. 



nitrogenous contents. When no material for forming cellulose exists, the 

 plant cannot grow; but in solution of pure su^ar in the absence of any 

 nitrogenous substance, the plant will multiply its cells for a certain time, 

 the protoplasm of the old cells being transferred into the new ones as 

 they are successively evolved. But under these latter circumstances the 

 cells become gradually smaller, and at length cease to multiply, a portion 

 of the nitrogenous matter being wasted in the reproduction until it be- 

 comes insufficient to carry on the growth. 



On the other hand, if sufficient nitrogenous matter exists, the fermenta- 

 tion goes on, accompanied by the production of a more developed form of 

 the mycelium, consisting of elongated interwoven filaments (the so-called 

 Vineyai<-plant) ; and development of this continues, if not interfered 

 with, until the liquid consists of little else but pure water. The final 

 form is the so-called " mother " of vinegar, which destroys the acetic 

 acid. 



There fs another mode in which the Yeast-plant is multiplied, and that is 



Fig. 587. 



X.800 



by endogenous segmentation of the cells. 

 The protoplasm divides by segmenta- 

 tion (fig. 593) into four subdivisions, 

 around each of which a new cell-wall is 

 secreted, as subsequently explained, 

 p. 585. This mode of multiplication may 

 be seen by placing a little yeast on a 

 thin layer of plaster of Paris beneath a 

 bell-glass so as to ensure sufficient mois- 

 ture. After a week or more the new 

 cells may be seen with a i object-glass. 

 In whichever way the multiplication 

 is effected it is clear that the .materials 



for SUCh increase niUSt be derived irom 



without the plant must feed; and 

 it has been found, experimentally, that it requires substances to build up 

 and renew its protoplasm or nitrogenous constituent, cellulose, or fatty 

 materials or carbo-hydrates, mineral matters (sulphur, &o.), and water. It 

 is not necessary that these substances should be in the food, simply that 

 the latter should contain the elements out of which they can be formed 

 by the plant. For experimental purposes Pasteur's solution * may be 

 used : this consists of a solution of sugar, furnishing the hydrocarbon, 

 ammonium tartrate supplying the requisite nitrogen, potassium phos- 

 phate, calcium phosphate, and magnesium sulphate yielding the requisite 

 mineral ingredients. The breaking-up of these ingredients, and their 



*$J*3f5*ISS8l 



liquid and smaller form on the 



surface of stale beer. 



* Pasteur's fluid : 



Potassium phosphate 

 Calcium phosphate 

 Magnesium sulphate 

 Ammonium tartrate 



Cane-sugar 1500 



Water... , 8576 



20 parts 



2 

 100 



10,000 



