236 DIVISION II. COURSE OF DEVELOPMENT OF FUNGI. 



is one of this kind. On the other hand, forms like Xylaria, which have Woronin's 

 hypha as a transitory formation only, offer transitions connecting them with Polystigma. 

 Amongst the former cases which connect with Melanospora are forms in which at one 

 end of the series distinct archicarps are present functioning as certainly asexual (par- 

 thenogenetic) ascogonia, and along with them distinct elements of an envelope ; towards 

 the other end of the series the difference between ascogonium and envelope-formation 

 diminishes till it disappears, and it is only in a more advanced stage of development 

 of the sporocarp that the formation of ascus and of envelope is undertaken by separate 

 elements, which up to that time were apparently uniform with the rest (Pleospora, 

 Claviceps). Sexuality therefore is not developed, and in the extreme cases there is 

 entire disappearance of primordia of the sporocarp which are homologous with sexual 

 organs. In the other series of cases Woronin's hypha in the Xylarieae can be under- 

 stood if we compare it with the archicarp of Polystigma or Collema. It occupies the 

 same morphological position, but takes no active part, as far as can be seen, in the 

 formation of the sporocarp, and then disappears apparently without having had 

 any function to perform, while the formation of the asci is undertaken by neighbouring 

 hyphae belonging to the envelope. Here then there is an archicarp or ascogonium 

 present in form, but it remains functionless in the sense expressed by these names, 

 and the formation of asci falls to the lot of other organs not strictly homologous 

 with it. 



These facts all lead to the result, that in these extreme cases we are in presence 

 of phenomena, which were spoken of above on page 1 23 as interruption and restoration 

 of the homology. Such a conception would perhaps be rash, if we had not before us 

 the clear cases above mentioned of the occurrence of this phenomenon in Ferns and 

 Angiosperms ; but, from our acquaintance with it there, we are led naturally to this 

 assumption by arguments which have now been stated. The species with an aborted 

 Woronin's hypha and a formation of asci at the same time are parallel to the 

 apogamous Ferns with functionless archegonia and to Angiosperms with an aborted 

 egg-apparatus replaced by adventitious embryos ; the rest approach nearer to simply 

 parthenogenetic apogamy, as seen in Chara crinita and the Saprolegnieae, but 

 with the peculiarity that the rrapdevos itself entirely disappears in the extreme cases. 



In the above discussions the simple forms which have distinct archicarps, such 

 as Eremascus, Erysiphe, and Eurotium, have been treated throughout as forming an 

 indivisible group of closely related species, and it has been sought to bring the rest 

 into connection with them. More is not at present possible. It ought not by any 

 means to be affirmed that all these forms which serve as points of departure are 

 connected with the same species outside the Ascomycetes, and that subordinate 

 parallel or diverging series do not proceed from individual forms among them inside 

 the circle of the Ascomycetes. It was shown above that Eremascus comes near 

 the Mucorini, and perhaps special groups of other Ascomycetes connect with 

 Eremascus. Podosphaera is nearer on one side to the Peronosporeae, on the 

 other to the main body of the Pyrenomycetes, and so on. But at present we are 

 not in possession of the empirical material necessary for the enquiry into these details, and 

 the main results, as here represented, are not decidedly affected by it. The resemblance 

 also in the development of the sporocarps which we have been considering to that of 

 the Florideae has necessarily always attracted attention, but whether it points to 

 an actual closer affinity must for the present remain undecided ; other connection 

 than that to which attention has been called above cannot in my opinion be established. 



