362 Blackman. — On the Fertilization , Alternation of 
sporophyte, is brought about in a purely apogamous way (as in the case 
of the Uredineae without an aecidium), perhaps by the interaction of two 
vegetative cells, as in the union of vegetative cells of the prothallium 
mentioned above. Maire (30) has stated that the basidiospore gives 
origin to a mycelium with single nuclei (thus agreeing with the sporidium, 
which has always been found to behave in this way), and that later in the 
mycelium the nuclei become paired, but in what manner is not known. 
The condition of paired nuclei seems in some cases to arise very early, for 
Harper (21) was unable to observe in Hypochnus any but binucleate cells ; 
the germination of the basidiospore, however, was not followed. 
The Basidiomycetes would thus seem to resemble very closely the 
lepto - forms among the Uredineae, where the mycelium has at first single 
nuclei but later develops paired nuclei in connexion with the formation of 
teleutospores, and like them would appear to have an alternation of genera- 
tions obscured , however , by the apogamous transition from one to the other. 
The fusion of nuclei in the basidium, like that in the teleutospore, 
is followed by a tetrad division, and there seems little doubt that it is also 
followed by a process of chromosome-reduction, or one corresponding to it ; 
the basidium, like the teleutospore, seems also of the nature of a spore- 
mother-cell, and is to be compared to that of the higher plants. The reduction 
in the basidium from four to two chromosomes described by Maire (30) as 
general for the Basidiomycetes can hardly be accepted, since these structures 
appear to represent groups of chromosomes, but the observations show clearly 
the analogy with Gymnosporangium. Whether the nuclear divisions in the 
Basidiomycetes will be found sufficiently typical to allow of the observation 
of an actual numerical reduction remains for future inquiry. 
Maire has also described a process of synapsis in the fusion-nucleus of 
the basidium, comparable to that here described for the teleutospore. 
Relationships of the Uredineae. 
It is obvious that the Uredineae and Basidiomycetes are very closely 
related, for both possess single nuclei during the early part of their life- 
history (starting from the teleutospore and basidium respectively), which 
later become paired. In both cases, also, the paired nuclei fuse in special 
reproductive cells, the fusion being followed by a process of synapsis, and 
then by a tetrad division 1 . The Basidiomycetes seem wanting in all trace 
of definite sexual organs, so that the Uredineae must be considered as by 
far the more primitive and cannot be treated as a mere class of the 
Basidiomycetes, as in the well-known classification of Brefeld. As pointed 
out in the previous section the latter group appear rather to be reduced, 
apogamous forms of the Uredineae. 
1 As is well known the transversely divided teleutospore of Coleosporium is practically indis- 
tinguishable from a transversely divided basidium. 
