DIV. I 



THALLOPHYTA 



439 



fructifications are completely wanting, probably owing to reduction. 

 The asci then arise directly from the mycelium. 



The ASCUS originates from a single cell ; this to start with contains 

 two nuclei, which fuse, and the resulting nucleus by repeated division 

 gives rise to eight nuclei. By a process of free cell formation the spores 

 become limited by cell walls in the way shown in Fig. 21 (Figs. 381, 

 391). In contrast to the formation of 

 spores in the sporangia of Phy corny cetes 

 the cytoplasm of the ascus is not com- 

 pletely used up in the formation of the 

 ascospores. The spores usually form a 

 longitudinal row, embedded in the remain- 

 ing epiplasnvwhich contains glycogen, and 

 are ultimately ejected from the ruptured 

 apex of the ascus by the swelling of this. 

 The spores are adapted for dispersal in 

 the air. 



a 



p, paraphyses ; sh, subhymenial 

 tissue. ( x 240. After STRAS- 

 BURGER.) 



In a few cases the eight nuclei before the 

 delimitation of the cells undergo further divisions ; 

 numerous free ascospores, e.g. 32 in TTiecotheus, 

 thus arise. More commonly divisions occur after 

 the spores are delimited, and result in the forma- 

 tion of eight bi- or multicellular bodies. 



The behaviour of the sexual nuclei in and after 

 fertilisation of the carpogonium is only accurately 



known in a few cases. For some Ascomycetes 



-, ,, \-4--u FIG. 381. Portion of the hymenium 



(Pyronema and Monascus] it has recently been Qf ^^ es<nde ^ \ Asci . 



shown that the sexual nuclei do not fuse in the 



carpogonium, but lay themselves side by side. 



In the ascogenous hyphae the pairs of nuclei 



divide conjugately, and only in the young ascus 



do two nuclei, the descendants respectively of a male and a female sexual nucleus, 



fuse together. Thus the conjugation of the sexual nuclei is here delayed from the 



carpogonium to the development of the ascus. 



So far as the results yet obtained allow of a conclusion being drawn, the 

 reduction division in the Ascomycetes happeus, just after the fusion of the two 

 nuclei in the ascus. 



In the life-history of the Ascomycetes an asexual reproduction by means of 

 conidia often precedes the development of the fructification. The conidia are spores 

 provided with a cell wall which are budded off from the tips of simple or branched 

 hyphae, the conidiophores (Fig. 384). 



According to the construction of the fructification we may dis- 

 tinguish in the first place the orders of the Erysibaceae, Plectascineae, 

 and Pyrenomycetineae, with closed or vase-shaped fruit-bodies (peri- 

 thecium), the Discomycetes with an open fructification (apothecium), 

 and the Tuberaceae with a fructification that is at first open but 

 becomes completely closed. 



