278 TEXT-BOOK OF FUNGI 



mother-cell called an ascus. In the greatest number of 

 species the ascus is elongated and narrowly cylindrical, and 

 the spores are arranged in a single row in the upper half of 

 the ascus. In others, again, the asci are broader in pro- 

 portion to their length, and the spores more or less arranged 

 in two rows. Departures from the most frequent type are 

 not uncommon. In the Tuberaceae the asci are frequently 

 globose, and contain a variable number of spores, and 

 frequently fewer than eight. 



In certain other species the ascus may contain sixteen, 

 thirty-two, forty-eight, or an indefinite number of spores. 

 In known cases the asci originate from hyphae that spring, 

 usually in considerable numbers, from a specialised cell or 

 oogonium, which certainly in some instances is a sexual 

 cell that requires to be fertilised before it gives origin to 

 the ascogenous hyphae. On the other hand, the paraphyses 

 and hyphae forming the perithecium or protective portion 

 of the fruit never originate from the sexual cell producing 

 ascigerous hyphae, but from other cells of the hypha bear- 

 ing the sexual cell, and situated immediately below it. 



The spores may be colourless or coloured at maturity, 

 globose, elliptical, fusiform, or needle-shaped; the surface 

 may be smooth, spinulose, warted, or covered with a raised 

 network. 



In the Saccharomycetes a single cell constitutes an 

 individual, hence in this family a protective structure or 

 perithecium, so characteristic of the group, is absent. In 

 the Gymnoasceae the peridium consists of very loosely 

 interwoven hyphae, which are often curiously branched, 

 and in some species bear specialised appendages, recalling 

 to mind the somewhat similar appendages springing from 

 the perithecia of many forms of the Perisporieae. 



