1 66 



INTRODUCTION TO THE STUDY OF FUNGI 



This group is allied to the Discomyceteac by such genera as 

 Sphaerosoma and Bcrgrcnnia, and analogous to the Gastromycetes, 

 especially Scleroderma, through the family of the Hypogeac. 



The hymenium consists usually of two kinds of organs, 

 which stand side by side, closely packed together ; these are 

 the asci and the paraphyses, but the latter are 

 sometimes, although rarely, suppressed. The 

 asci are essentially membranaceous, delicate, 

 colourless sacs, mostly closed, but occasionally 

 dehiscing at the apex by an operculum or lid, 

 more commonly irregularly ruptured, to permit 

 of the escape of the sporidia. These asci have 

 either a clavate form, with a more or less 

 elongated base, or they are cylindrical, of nearly 

 equal breadth throughout, except at the base, 

 where they are narrowed downwards to the 

 dimensions of the supporting hypha. In some 

 families, such as the Fej^isporiaccae, as well 

 as in the Tuber aceae, a form of ascus prevails 

 which approaches to globose or pear-shaped. 

 All forms of asci are usually very numerous 

 in each hymenium, but the globose are less so 

 than the clavate or cylindrical. The form that 

 is peculiar to any species is persistent in that 

 species, so that the form and approximate 

 size are relied upon as having value in the 

 determination of species. Whatever the form 

 each ascus assumes, it normally encloses eight 

 sporidia, or some multiple of eight — as sixteen, 

 thirty-two, etc. — occasionally only four, more rarely only 

 two, and very rarely indeed only one. In cylindrical asci 

 the sporidia may be expected to range themselves in a 

 single row, but in clavate asci they are either biseriate or 

 irregularly grouped towards the upper portion of the ascus. 

 By far the larger number of sporidia are continuous, consisting 

 of a single cell, and range from a globose to an elHptical form, 

 especially in the Discomyccteae, whilst in the Pyrenomyceteae 

 greater variation prevails. Doubtless all the forms of sporidia 

 are at first continuous, and acquire septa as they approach 



Fig. 68.- — Asci aud 

 paraph yses. 



