CHAPTER V. — COMPARATIVE REVIEW. — ASCOMYCETES. 237 



A nearer approximation of the Ascomycetes generally, or of some of them, to the 

 Florideae would not materially affect the conclusions at which we have arrived above 

 with regard to the main questions connected with the homologies. 



In my first investigations (Beitr. Ill) into the development of the sporocarps in 

 Erysiphe, Eurotium, Pyronema, and others I called the archicarps and antheridial 

 branches generally sexual organs ; and from the great amount of agreement between 

 the sporocarps when fully formed I expressed the conjecture that all the Ascomycetes 

 have homologous and analogous organs for the production of these sporocarps. 

 Others followed me in this view, especially when they became acquainted with 

 individual cases which confirmed it. The investigations which are here communicated 

 have had the result of showing that my generalisation was incorrect, and that the mistake 

 arose not merely from want of consideration of facts nofthen known, but more especially 

 from not distinguishing sufficiently between morphological and phylogenetic homology 

 and physiological analogy. I trust that 1 have taken this distinction sufficiently 

 into account in my last special treatise (Beitr. IV) and in this work. 



Van Tieghem has been one of the chief opponents of my view, for he takes his 

 ground on forms that have no distinct archicarps and does not allow of ' sexuality ' 

 in the Ascomycetes. His opinion briefly stated is* this, that the differentiation of 

 the ascogenous hyphae and their envelopes takes place at stages in the development 

 of the sporocarp which vary according to the species, and that it occurs at the earliest 

 possible stage in the species which are supposed to have sexual organs. The supposed 

 female organ is only an ascogenous hypha differentiated at a very early period, the 

 supposed male organs are simply part of the envelope-structures. The facts on which 

 Van Tieghem originally founded his opposition were certainly not happily chosen. 

 But if he is content to rest his case on Pleospora for instance, or even on the actual 

 condition of things in Sclerotinia with which he has never been acquainted, he must 

 be allowed to be quite in the right as against my original conjectural generalisation 

 literally taken ; and if he objects that the actual sexual function of these organs has 

 not been proved in the case of Eurotium and Podosphaera, he will find that this 

 is allowed in my work of 1870. But Van Tieghem makes no enquiry into the 

 homologies and extends his negation beyond the limits allowed by the facts. If 

 he had duly considered the indisputable fact of the constant presence in Podosphaera 

 of my antheridial branch, that is of an organ distinctly different from the later- 

 formed structures of the envelope and accompanying the proper commencement of 

 the sporocarp, he would have been led to those true subjects of enquiry which 

 have been discussed in the foregoing pages, and which it has been attempted to elu- 

 cidate ; and the facts at present known about Pyronema, Eremascus and other forms 

 should have led him to a different answer to his own enquiries. We need not go 

 into his positive views with regard to the function of the organs in question, that, 

 for instance, the antheridial branches serve to support the ascogonium and that the 

 trichogyne in Collema is an organ of respiration, before it has been shown to be to 

 some extent probable that the ascogonia are in danger of falling without this support, 

 and that the particular organ in Collema is obliged to have an apparatus of its own 

 to get air, and cannot respire without it quite as well as the elements of the interior 

 of the thallus near which it is placed. Such fancies must certainly deserve the 

 name of gratuitous hypotheses quite as much as the views which I have here 

 explained. 



Another opponent of my ideas is Brefeld. He wavers between Van Tieghem's views 

 on the one hand 1 , and certain others, which, when stripped of some accessories which 

 do not strictly belong to the question, agree with those of the present work 2 . I have 

 therefore no reply to make, apart from the corrections of some matters of fact 



1 Bot. Ztg. 1876, p. 56, Abs. 23, and Schimmelpilze, IV, p. 142. 



2 Bot. Ztg. 1877, p. 371, and Schimmelpilze, IV. 



