272 BOTANICAL GAZETTE [APRIL 
which fuse are apparently equal gametes. If we consider the matter 
simply from this standpoint, the whole sorus must be considered as 
a collection of such pairs of equal gametes. The fusion of each pair 
should form a zygospore like that of the lower molds. There are, 
however, two important differences. The product of the fusion in 
the aecidium is a temporary structure which germinates at once, and 
further, in germinating it produces a considerable number of spores, 
the aecidiospores, while in the mold normally only one zygospore 
is produced. If it is found that the same method of fusion occurs in 
Micropuccinia this form might be considered an intermediate stage 
between the molds and Eupuccinia. 
Further, it seems plain that each pair of gametes with the spores 
produced by them constitutes an individual structure. The aecidium 
cup, which has so often been considered the individual fruit body on 
account of its likeness to the cystocarp or pyrenocarp, is shown, by 
the discoveries described above, as well as by those of BLACKMAN, to 
be a complex of coordinate units rather than itself a morphological 
unit. An ascocarp is the product of the fusion of a single pair of 
gametes, while the aecidium arises from a collection of many such 
fusing pairs. Further, the peridium of an aecidium cup is not to be 
compared to the perithecial wall of the ascocarp, since it is composed 
of rows of cells which are morphologically equivalent to the aecidio- 
spores. The tissue protecting the asci, on the other hand, is pro- 
duced by the massing together of vegetative filaments which do not 
arise from the fertilized egg. : 
I am convinced that the method of conjugation above described 
will be found in the forms with the limited cup as well as in the more 
indefinite aecidial sori of Caeoma. Considering the aecidium a 
collection of individuals, it would seem that those forms having @ 
peridium are to be regarded as the more highly specialized, while 
the caeoma is the more primitive type. ; 
Against these views, which seem to me the obvious conclusions 
be drawn from my discoveries, it may be urged that the spermogom 
with their spermatia, showing as BLACKMAN points out very man} 
resemblances to the male cells of the lichens and the red algae, 4° 
still left unexplained, and it must be admitted that there is ground for 
BLACKMAN’S suggestion of the origin of the rusts from the red algae. 
