214 BOTANY. 



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

 an hour, 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 ScJiizomycetes are the species of Sac- 

 cliaromyces which produce fermentation in sugar solutions. 

 The type of the genus is Saccharomyces cerevisice, 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 modification of fission), a small daughter-cell being 



formed by the side of the 

 mother-cell, and sooner or later 

 separating from it (Fig. 146, a, 

 V). The other form consists of 

 larger cells, which, by a division 

 of their protoplasm, form four 

 new cells within the parent-cell 

 Fig. i46.-The Yeast plant, .Saccha- (Fig. 146, c, d). This is probably 



romyces cerevwice. a, rounded cells v 



from " bottom yeast," 50 hours after no more than the ordinary pro- 

 cowing in beer- wort; 6, row of oval . .. -,-.... 

 cells from "top yeast;" c, "bottom C6SS of internal Cell-dlVlSlOn, 

 yeast " after cultivation on a piece of ,,, i . i r. J.T vj. 

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

 rior of the parent cell; d, the four - i <> _ roQ + or imnnrtaripp t 

 daughter-cells, a and 6x400, c and d tO D6 OI gl eater impOltance.J 

 X 760,-After Reess. Thig f orma ti on 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 phos- 

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

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

 to be omitted in some cases. 



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

 mentary Biology," Chap. IV., for directions in making his observations. 



t Reess, in his " Botanische Untersuchungen iiber die AlcoholgUh- 

 rungspilze," 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 ! 



