164 



BOTANY 



granular vacuolated cytoplasm. The two nuclei fuse into a single 

 one, which then undergoes repeated divisions until eight free nuclei 

 are formed. At the poles of the nuclear spindle there is a con- 

 spicuous "aster" of radiating fibres. Each free nucleus has close 

 to it a well-marked aster which persists after the division is com- 

 plete (Fig. 127, E-G). The nucleus develops a beak from which 

 the aster-fibres radiate. The latter next arrange themselves in the 

 form of a wheel about the beak of the nucleus and gradually increase 

 in length and finally cut out a nearly spherical mass from the cyto- 

 plasm, which encloses the nucleus, and thus forms the young spore. 

 A firm wall is developed about the spores, which are imbedded in 

 the remaining cytoplasm of the ascus (G). 



FIG. 128. Dipodascus albidus. Development of the ascus. (After LAGERHEIM.) 



(X500.) 



SUBCLASS I. HEMIASCINE^E 



The Ascomycetes may be divided into two subclasses, the Hemi- 

 ascineae, in which the spores are produced in large numbers within 

 the ascus, and the Euascese, where the number of ascospores is, with 

 few exceptions, regularly eight. The Hemiascineae are few in num- 

 ber, parasites or saprophytes. Their reproduction is for the most 

 part non-sexual, but in the peculiar genus Dipodascus (Fig. 128) 

 there is a fertilization of an oogonium by fusion with the anther- 

 idium, the fertilized oogonium developing into an ascus containing 

 numerous spores. In the genus Protomyces, which is not always 

 placed among the Ascomycetes, the numerous spores formed in the 

 asci (?) fuse in pairs before germination, much like the gametes of 

 the lower Algae. 



