CHAPTER V.—COMPARATIVE REVIEW,—USTILAGINEAE. I 83 
--The strongést argument which could be advanced at the present time in support 
of Brefeld’s view is, that, according to his statements, species like Ustilago longissima 
show pairing in the ‘ gonidia’ which are produced in nutrient solutions and sub- 
sequent formation of mycelial primordia under the given conditions, while pairing 
is not observed when germination has taken place in water. But the course of 
development is not perfectly known in these species, and they cannot be a standard 
for judging of those which are thoroughly known. And what we know about these 
species, especially Ustilago longissima, gives ground for suspecting that even in them 
pairing is a necessary preliminary to the formation of mycelial primordia capable of 
infection, and that it occurs in opposition to the case of Tilletia only under special 
conditions of nutrition which have yet to be ascertained. 
In whatever way the question of the sexual value of the pairing may ultimately 
be decided, it is at all events a characteristic fact in the cases in which it occurs and 
cannot be disregarded. 
The homologies in the course of development of the Ustilagineae are quite clear 
within the group itself, and require no further discussion. It is moreover obvious, 
and the fact is expressed by the terminology which has been partly anticipated, that 
this development corresponds in general to that of the preceding groups, and resting- 
spores therefore may be compared with the resting-oospores, oospores or carpospores 
of the Peronosporeae and Entomophthoreae, &c.; the comparison of the simpler 
forms, especially Entyloma and Tilletia, confirms this view. If this comparison is 
accepted, we have at once a justification of such terms as gonidia, &c. The resting- 
spores or carpospores, as they may be presumed to be, of the Ustilagineae are 
formed, it is true, asexually, while the contrary is the case with those of the Perono- 
sporeae; but this, as we have learnt from the Saprolegnieae, affords no criterion for 
the determination of the homologies. It is not easy to see why it should be the 
Entomophthoreae particularly to which the Ustilagineae must be considered to 
approach nearest, as Brefeld maintains’; it might very well be the Peronosporeae. 
But while the agreement between the groups makes itself thoroughly felt, a near 
approximation of them is in most points impossible; this can be brought about in 
many places, if we put one thing forward and disregard another, but we gain 
nothing by these arbitrary proceedings. If, on the other hand, we look for the points 
which are distinctly characteristic of the Ustilagineae, the most prominent is that of 
the conjugating pairs of cells. This phenomenon recurs, so far as is known, only 
in one form not belonging to the Ustilagineae at the same place in the course of the 
development and in a quite similar form, namely, in Protomyces macrosporus. There 
is only one important difference between the two cases; in Protomyces the con- 
jugating cells are of endogenous origin, in the Ustilagineae they are acrogenously 
abjointed, but this difference is no real objection to the homology, for it occurs in a 
similar form among the undoubtedly homologous gonidia in the Mucorini 
(section XLII); the pairs of cells in Protomyces are formed endogenously, like 
‘the gonidia of Mucor, those of the Ustilagineae acrogenously, like the gonidia of 
‘Chaetocladium. Hence Protomyces macrosporus appears to be in every respect very 
nearly related to the Ustilagineae, and its resemblance in habit to species of Entyloma 

1 Brefeld, Schimmelpilze, IV, p. 165. 
