CHAPTER V.—COMPARATIVE REVIEW.—ASCOMFCETES. 239 ; 
antheridial branches and sometimes spermogonia with spermatia, 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 
Sormations of gonidia are intercalated between them. These formations make their 
appearance sometimes as a /ransitory 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. 
(4) 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. 1. There is nothing to add here to what has been already said 
of the archicarps 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}. 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. 
