CHAPTER V. — COMPARATIVE REVIEW.— ASCOMYCETES. 233 



above. These comparisons show that archicarps, antheridial branches, and all other 

 parts of the same name in all the Fungi which are here compared, are homologous. 



The homologies go as far as the archicarp ; they cease with its further de- 

 velopment, unless we may perhaps compare the oospore of Cystopus which forms 

 swarm-spores directly in germination (page 135) with an ascus; the ascus of 

 Podosphaera and Eremascus is an organ which does not appear in the Peronosporeae, 

 and this may be said still more of the sporocarp of Erysiphe and the series of forms 

 which follow it. The series of the Ascomycetes and that of the Mucorini and 

 Peronosporeae set out on divergent routes from Podosphaera and Eremascus, as the 

 members which touch one another in the two series. It must not be forgotten 

 that in this comparison of sporocarps, the parts spoken of above as the ascus- 

 apparatus are alone to be taken into consideration, and have been considered here. 

 The envelope-apparatus, important as it is in other connections, does not enter into the 

 question. For the case is exactly the same if there is no envelope-apparatus, as 

 really happens in Eremascus, and would be the same if there were Peronosporeae 

 with their oogonia in envelopes ; this, it is true, has not been observed, but it is quite 

 possible, and in Mucorini (see section XLII) the zygospores are provided with 

 envelope-apparatus of great variety of form. 



When once the homology between the archicarps of the two groups is proved, 

 that of all the spores, which have been termed gonidia in the preceding pages, is 

 also established. The expression was anticipated above throughout in the case of 

 the Ascomycetes, so far as it was supposed to have exactly the same meaning as 

 in the Peronosporeae and their nearest allies. 



In the Peronosporeae the antheridial branch and the archicarp function 



as sexual organs. But homologous members need not also function in all cases 



as exactly similar organs, as appears at once from the case of the Saprolegnieae with 



doubtful sexuality and with sexuality undoubtedly wanting. Hence when the homology 



has been established it is still an open question, whether the members of the 



Ascomycetes in question are sexual organs or not. To understand clearly this 



much discussed question 1 we must first of all remember that, in our imperfect 



knowledge of the nature of sexuality and the sexual process of fertilisation, we 



have no simple mark or reagent by which we can recognise the sexual quality 



of an organ. We learn from the facts before us that in every process of fertilisation 



there is a material union of one peculiar male or fertilising cell or at least of 



a portion of its protoplasmic and nuclear substance with one other, a female 



cell, which is to be fertilised, or, as in the Florideae, with a pluricellular female 



apparatus 2 . The result of this union is that the female portion is rendered capable 



of further development : the development does not take place without this union, and 



union with the male portion is necessary that the female may become capable of 



it. In a doubtful case therefore the determination will depend first on the observation 



of the union of the protoplasm or nucleus, and secondly on the experimental 



proof of the necessity of this in order that the presumed female portion may become 



1 See Beitr. IV, pp. 74, HI. We cannot enter here into a discussion of the general question of 

 sexuality; the beginner is referred to Sachs' Text-book, 2nd Engl. ed. 



2 See the work cited on page 213, and Fr. Schmitz in the Monatsbericht d. Berliner Acad. 1883. 



