CHAPTER V.—COMPARATIVE REVIEW.—-ASCOMFCETES. 231 
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! 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 

! Stahl, Beitr. z. Entw. d. Flechten, pp. 30, 38. 
