SECT. I 



CRYPTOGAMS 



391 



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 

 perithecia occupy an isolated position. 



Order 1. Erysipheae (Mildew Fungi) (^^^ *'^). 

 The small spherical perithecia have a closed investment (peridium) which 

 ultimately opens irregularly and liberates the ascospores. The asci stand 



singly or in a group in the centre of the fruit. 



The Erysipheae live as 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 myceliuui also 

 inhabits the intercellular spaces of the leaf. 

 The ripe ascus fructifications (perithecia) are 

 small black bodies provided with peculiar 

 appendages. In the simplest forms [e.g. in the 

 genus Sphacrotheca) the spheroid perithecium 

 encloses only a single ascus with eight spores. 



Pig. 319. — Utwiuula nccator. A, Conidial 

 stage ; c, coniilium ; h, conidiophore. B, 

 Hypha which has formed a disc of attach- 

 ment (a) and lias sentahaustoriuni (/()iiito 

 an epidermal cell. C, Perithecium with 

 appendages. (From Soraueb, Lindau, 

 and Reh. Hamlb. d. PJlanzenkrankheiten, 

 ii. p. 104. moii.) 



FiLi. 320. — Oouidiophores of Afperriillus herbarioruvi (to the 

 left) and Petiicillium crustaceiim (to the right). 



It is enveloiied by a covering of sterile hyphae, forming a sheathing layer, two to 

 three cells deep. The genera Enjsiphe and Uncinula, on the other hand, develop 

 sevei'al asci in each perithecium, and in Phyllactinia 12 to 25 asci are present. Since 

 all the eight nuclei are not utilised in spore formation the number of spores in 

 each ascus is usually 4 or only 2. The 2:)erithccia are irregularly ruptured at their 

 apices and the spores are thus set free. As HAKPEiiiias shown, the first rudiment 

 of the perithecium consists of an oogonium and an antheridium. The.se are 

 uninucleate cells, separated from the mycelium by partition walls, and stand close 



