214 



BOTANY. 



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

 an hour, and then filterinfj; the filtrate will, if kept at tlie ordinary 

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

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



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

 without sugai', the previously clear liquid is soon made turbid by the 

 rapid increase of Bacteria.f 



279. — Allied to the Scliizomycetes are the species of "Sac- 

 charomyces 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, 

 i). The other form consists of 

 larger cells, which, by a division 

 of their protoplasm, form four 

 new cells within the j)arent-cell 

 (Fig. 146, c, d). This is probably 

 no more than the ordinary pro- 

 cess of internal cell-division, 

 although it has been thought 

 to be of greater importance. J 

 This formation 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. 



Fig. 146.— The Yeast Plant, Saccha- 

 romyces cerevisiiB. a. roundfd cells 

 from " bottom yeast," 50 hours afier 

 sowing in heer-woi-t ; 6, row of oval 

 cells from ^'top yeast;" c, "bottom 

 yeast" after cultiva'ion on a piece of 

 carrot, four cells forming in the inte- 

 rior of the parent cell ; d, the fonr 

 daughter-cells, a and 6 X 400, c and d 

 X 760.— After Recfs. 



* 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. 



t The student may profitably refer to Huxley and Martin's "Ele- 

 mentary Biology," Cliap. IV., for directions in makinsrhis observations. 



J Reess, in bis " Botanische Untersuchungen iiber die Alcciliolgah- 

 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 1 



