136 COMPARATIVE MORPHOLOGY OF FUNGI 



part (Fig. 83) ; consequently the asci are united into a broad continuous 

 layer, a hymenium, which in certain forms, especially lichens, can 

 occasionally continue its growth for years. By this lateral development 

 of the fertile part, the top of the fructification is ruptured into shreds, 

 so that at maturity the hymenium is exposed. As with the perithecia, 

 the asci in the apothecia are generally imbedded between paraphyses 

 (Fig. 83) ; at times, as in certain Geoglossaceae, these arise in special rich 

 storage cells similar to the auxiliary cells of the Florideae and hence 

 show their primary function as nutritive organs. 



Corresponding to the open position of the mature asci, the violence 

 of ascospore discharge has undergone a considerable increase. In several 

 groups, the top of the ascus opens like a cover whereupon the ascospores 

 are shot out with great force (in Ascobolus immersus up to 35 cm. high), 

 and, as in the perithecia, are given over to an anemochoric dissemination. 

 As in the discharging perithecia, so also in the discharging apothecia, all 

 spores of one ascus remain clinging together by gelatinous shreds or 

 sheaths, so that an enlargement of the discharged mass is attained; thus 

 the volume of one of these spore balls of Ascobolus immersus is about 2,000 

 times larger than that of a basidiospore (Buller, 1909); thus may easily 

 be explained the greater momentum with which these fungus "cannons" 

 shoot off their projectiles. As in many discharging perithecia, e.g., those 

 of Endothia, so also in many discharging apothecia, the activity of the 

 asci is largely dependent on external influences (Falck, 1916); still others 

 react chiefly to mechanical stimuli, as those which are liberated by cur- 

 rents of air or wind (Falck, 1923). 



Systematic classification of the Ascomycetes rests upon the degree of 

 development of the dicaryophase. Those forms in which the dicaryo- 

 phase is lacking and in which the sexual cells and ascus arises directly 

 as the product of a sexual act are called Hemiascomycetes; those 

 forms in which the sexual organs (Thelebolus and the Laboulbeniales 

 excepted) developed to ascogenous hyphae which in turn are adapted to 

 the formation of numerous asci are called the Euascomycetes or typical 

 ascomycetes. We will discuss briefly, in the review at the close of the 

 Ascomycetes, the probable phylogeny of these two subclasses and the 

 phylogenetic derivation of the Ascomycetes as a whole, when the reader 

 will have oriented himself in the various forms. 



