CHAPTER V. COMPARATIVE REVIEW. ASCOMYCETES. 2$\ 



of forms, in the other with two species with fewer forms and in other respects like 

 one another. 



SECTION LXVI. The remarks which have now been made render it un- 

 necessary to say anything more concerning the homology of members of the same 

 name in the Ascomycetes which we are here considering; nor need we further 

 discuss the fact, that the mature sporocarp contains in some cases only the products 

 of the development of one archicarp, in others, as in Physma and Pyronema, the 

 results of the development of several archicarps. We could if necessary establish 

 sub-forms on this distinction. The question of the homology of the spermatia and 

 spermogonia is not so readily settled; but even here the difficulties are not great. 

 It may be conceded that the consideration of the function of the spermatia of the 

 Collemaceae puts us on the right track. That function, as will be shown in the 

 following section, is the same as that of the antheridia in other and allied species. 

 Hence arises the consideration whether the spermatium with the spermatio- 

 phore, the sterigma, is not the homologue of an antheridial branch from which 

 portions are abjointed in the form of spermatia, according to the arrangements of 

 particular species, in order to be capable of the fertilising function. Forms like 

 Collema, in which spermatia and archicarps are formed at a distance, from one 

 another, may not afford any sure ground for an answer to the question; but the case 

 is different with Physma, where spermatia and archicarps spring close together from 

 branches of the same hyphal coil, like the antheridia and archicarps of Pyronema. 

 If the spermatia in Physma remained fixed to their spermatiophores in order to 

 conjugate with the archicarp, the only difference between the two forms would be 

 that of conformation. The actual differences, it is true, go farther than this, since the 

 spermatiophores are combined into a spermogonium from which the spermatia are 

 discharged, and the archicarps are outside of it, and send up the trichogyne to 

 the place where it encounters the spermatia. But we can understand all these 

 phenomena as adaptations to suit the origin of the two organs inside a dense 

 thallus which impedes their direct meeting, and still maintain the homology with 

 Pyronema. Even the excessive numbers of the spermatia or antheridial branches 

 will be quite intelligible in view of the very general rule that the number of male 

 sexual cells in a species increases with the difficulties in the attainment of its 

 physiological aim. But homology of the spermogonia and archicarps of Physma 

 with those of Collema is quite obvious ; the latter agree perfectly with the former in 

 every respect except in their diclinous and monoecious distribution, which in some 

 forms 1 inclines to dioecism. But this arrangement is no difficulty in the question 

 before us, since diclinism may appear everywhere and is actually observed in 

 many species, in which sexual cells are endowed with free motion whether active 

 or passive. 



It follows from these comparisons and considerations that in Collema also the 

 spermatia with their spermatiophores may properly be considered to be homologues 

 of the antheridial branches and antheridia of more simple forms, and the pecu- 

 liarities of their development, and the excessive numbers in which they are produced 



1 Stabl, Beitr. z. Entw. d. Flechten. pp. 30, 38. 



