SECTION XII. 



FORM, .STRUCTURE, AND CilKMlCAJ. COM I'c^STTTOX 

 OF THE YEAST CEJ.L. 



rirAITKK XL VI. 

 MORPHOLOCJV AND LliE-lilSToK V UK TIIK YEASTS. 



^ 243.— Position of the Saccharomycetes in the 

 Botanical System. 



It was st^it^a in ^^ .^20 that only a few classes of the sub-kin-doni 

 of Mycoinycetes exl.ibit the faculty of producing en.lo<'enous 

 spores nau.ely the Asconiycetes. Conse<iuentlv the latter may he 

 detined as endosporogeuic Mycomycetes. In' the Siinie plac'e it 

 was also mentioned that the organ wherein the endogenous 

 spores are fonued in this class is not called a sporangimn but 

 an ascus, and ditlers from the sporangium b..th as re.'iu-ds the 

 greater fixity of shape and also the number, shape, and method 

 ot tormation of the spores therein contained. These spores ;ue 

 tlieiebue called ascospores. 



The fundamental characleristic distingui>hing the ascus fi-om 

 the sporangium resides in the behaviour of the be^irer of the 

 inherited properties of the organism, namely, the cell nucleus 

 .luring sporulation. The sporangium (p. i , ) is polvnudenr from 

 the outset, whereas the ascus cont^iins only a single nucleus at 

 the commencement of sporulation. The nucleus-as will be 

 more fully descnbe.l in .^ 250— repruluces bv suWivision into as 

 many .laughter-nuclei as there will be ascospores. In the sporm- 

 ,'uim, on the other hand, as many nuclei as there will subse- 

 quently be endo.sporesare transferred from the aseptate mycelium 

 to the sporangium before the s.'parating membmne is formetl 



It is only ,n the least highly .leveloped Asco„nreh',< that the 

 ascus springs ,lirect from the mycelium ; in all 'the rest it is 

 developed m or upon a special organ called the carpoascus, and 

 all the AscoiuN-c-etes fructifying in this manner are grouped into 

 the sub-class of Carjx>a.<cen: Antithetical to this class are the 

 Unver Asromi/ctes, the Gi/muoa^ceo', the asci of which tu-e nake«l • 

 and it IS to this latter group that the most of the t<?chnioillv 

 unportiint yeasts belong. 



An examination of the development of the caipa-usci of a 

 uumlKH- of species belonging to the first sub-class has revealeti 



