CHAPTER V. — COMPARATIVE REVIEW. — ASCOMVCETES. 239 



antheridial branches and sometimes spermogonia with spermatid, as in Pyronema, 

 species of Ascobolus, and Collema. This may be called the simple course of 

 development in the Ascomycetes. 



2. The dimorphous or pleomorphous course of development. Similar 

 to the simple one in the terminal points being represented by the ascospores, but 

 formations of gonidia are intercalated between them. These formations make their 

 appearance sometimes as a transitory intermediate generation (Polystigma), sometimes 

 as precursors of the ascocarp on the same thallus, and capable under favourable 

 conditions of uniform reproduction through an unlimited number of generations. 

 Excellent examples are Erysiphe, Eurotium, Penicillium, Sclerotinia Fuckeliana. 

 The gonidia are usually acrogenous, seldom intercalary also, in their abjunction, 

 and are produced — 



(a) On solitary simple sporophores, or sprouting cells. 



(<5) On the exposed upper surface of compound sporophores, as in Claviceps. 



(c) In peculiar receptacles, pycnidia (pycnogonidia, pycnospores, 'stylospores '). 



Each species can only produce one of these gonidial forms, as is the case with 

 Erysiphe, or under favourable conditions more than one, as Pleospora and Nectria. 



In all cases that have not been thoroughly examined and are therefore more or 

 less doubtful, an organ or member of the development must be determined and 

 named according to the agreement of its observed characters with those of thoroughly 

 known forms. The correctness of the naming will be more or less certain according 

 to the degree of agreement, and will vary from the extreme of probability to entire 

 uncertainty. The result of this examination of the separate parts and organs is as 

 follows : — 



Section LXVIII. i. There is nothing to add here to what has been already said 

 of the archiearps and antheridial branches. 



2. The sporocarps (apothecia and perithecia) with the asci agree so entirely in 

 the essential points of structure, development, and moment of appearance in the 

 general course of the development, as they are known to us and have been described 

 above, that, as has already been pointed out, they may or must be regarded as generally 

 homologous in the sense and with the modifications above indicated. In by far the 

 largest number of species, as far as our experience goes, they are the most constant 

 members in each species in their structure and especially in the structure of the asci 

 and ascospores. Exceptions to this rule, in which the number or size of the spores 

 is strikingly unequal in different asci, are comparatively rare, and some instances have 

 been mentioned above on page 79. Similar cases are recorded in Pleospora and 

 some other forms. Calosphaeria biformis, Tul. and Cryptospora suffusa, Tul. are 

 said to have two kinds of perithecia, one of which has asci with a large number of 

 small spores, the other asci with from four to eight much larger spores 1 . How far this 

 is really a case of difference within the same species, and not also of the mixing up 

 of two similar or associated species, should be enquired into, and the investigation is 

 rendered more necessary by the question which has arisen in the case of Pleospora 

 noticed on page 230. 



1 Tulasne, Carpol. II. 



