SECT, i CRYPTOGAMS 389 



organs occur in some Ascomycetes (e.g. Polystigma) which do not 

 form parts of Lichens. 



3. Pyronema (Fig. 333) and related genera together with 

 Boudiera ( c2 ) exhibit a quite distinct type. A multinucleate carpo- 

 gonium which is provided with a trichogyne is fertilised by a multi- 

 nucleate antheridium, the two structures being thus coenogametes. 



4. In the Erysipheae (Fig. 328) a uninucleate antheridium unites 

 directly with a uninucleate oogonium. 



It remains for future research to determine whether these types 

 are to be derived from a single one or whether they indicate a 

 polyphyletic origin for the Ascomycetes. 



In many genera the sexual organs are more or less reduced, and 

 in some groups of Ascomycetes they are completely wanting. 



Ascogenous filaments which bear the asci on their ultimate 

 ramifications (cf. Fig. 334) arise from the carpogonium. Sterile 

 hypha? which arise from below the carpogonium also take part in 

 the formation of the fructification, forming an investment to it and 

 paraphyses standing between the asci. The two sorts of hypha are, 

 however, clearly distinguishable. 



The orders of Ascomycetes are provisionally characterised by the 

 construction of the fructification. 



In the Perisporiaceae the small, spherical fruits (perithecia) are 

 surrounded by a complete investing layer, on the rupture or rotting 

 of which the spores are set free. 



In the Discomycetes open cup-, club-, or hat-shaped fructifications 

 (apothecia) are formed ; the asci are arranged parallel to one another 

 in a superficial layer termed the hymenium. 



In the Pyrenomycetes the perithecia are flask-shaped, the asci 

 springing from the base of the cavity. 



In the Tuberaceae the subterranean, tuberous fructifications are 

 closed. 



To these orders must be added the Exoasci, in which the asci 

 arise from cells of the mycelium without the formation of any 

 fructification, and the very simple Saccharomycetes or Yeast-Fungi. 

 These two groups can be regarded as extremely reduced Ascomycetes. 



The Laboulbeniaceae in which the asci are enclosed in small peri- 

 thecia occupy an isolated position. 



Order 1. Perisporiaceae (**< (il ) 



This order, which includes only Ascomycetes with enclosed fructifications, com- 

 prises two families : the Erysipheae or Mildew Fungi and the Perisporieae. 



1. The Erysipheae form a family of distinctive, epiphytic parasites whose 

 mycelium, somewhat resembling a cobweb, and ramifying in all directions over the 

 surface, particularly the leaves, of higher plants, sends out haustoria which 

 penetrate the epidermis of the host. In some cases the mycelium also inhabits 



