CHAPTER V. COMPARATIVE REVIEW. USTILAGINEAE. 183 



The strongest 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 1 ; 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 XLIII) ; 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. 



