214 BOTANY. 



of cut Imy or any other similar vegetable substance in warm water for 

 an hoar, and then filtering; the filtrate will, if kept at the ordinary 

 temperature of a room (20° C), and allowed free access of air, become 

 turbid with Bacteria in the course of one or two days. 



(c) By adding a drop of the hay infusion to Pasteur's solution,* made 

 without sugar, the previously clear liquid is soon made turbid by the 

 rapid increase of Bacteria.f 



279. — Allied to the 8cMzomycetes are the species of Sac- 

 charomyces which produce fermentation in sugar solutions. 

 The type of the genus is Saccharomyces cerevisim, the yeast 

 plant (Fig. 146). It presents two conditions : in the first it 

 is in the form of transparent round or oval cells, averaging 

 .008 mm. (.0003 inch) in diameter ; these reproduce by bud- 

 ding (a modificatioiii of fission), a small dattghter-cell being 



formed by the side of the 

 mother-cell, and sooner or later 

 separating from it (Fig. 146, a, 

 i). The other form consists of 

 larger cells, which, by a division 

 of their protoplasm, form four 

 new cells within the parent-cell 



Fig. 146.— The Yeast Plant, S'JccAa- CTTicr 1 4fi /■ fl\ This ics nrnhiihlv 

 ramyees cerevisim. a. rounded chIIs l-^ 'g- J-*0> C, a;. xniS IS piODaOiy 



froin " bottom yeast," 60 hours after no more than the Ordinary pro- 



eowinff in neer-wort ; 6, row of oval j> - i i • • • 



cells from "top yeast ;" c, " bottom cess of internal cell-division, 



yeast" alter cultivation on a piece of i,, i -j i i ,-i i , 



■carrot, four cells forming in the inte- although it haS been thought 

 rior of the parent cell ; d. the four j. i j; j. ■ j x 



daughter-cells, a and 6x400, c and (i to be 01 greater importance.^ 

 X 750.-AfterHee8s. rpj^-g fomiation of new cells by 



internal cell-division appears to occur only when the supply 

 ■of nourishment is less abundant, as when the yeast is grown 

 on cut slices of potato or carrot. 



* Made as follows : Potassium phosphate, 20 parts ; calcium phoa- 

 'phate, 2 parts ; magnesium sulphate, 3 parts ; ammonium tartrate, 

 100 parts ; cane sugar, 1500 parts ; water, 8376 parts. The sugar is 

 to be omitted in some cases. 



■)■ The student may profitably refer to Huxley and Martin's "Ele- 

 imentary Biology," Chap. IV., for directions in makinjr his observations. 



X Reess, in his "Botanische TJntersuchungen Tiber die Alcoholgah- 

 Tungspilze," 1870, calls this process the formation of ascospores, the 

 mother-cell he calls an ascus, and the daughter-cells true ascospores. 

 Accordingly he considers these plants to be very simple Ascomycetes ! 



