36 Blackman and Fraser . — Further Studies on the 
by Christman (3), in which he showed that in certain forms ( Phragmidium 
speciosum , Caeoma nitens , and Uromyces Caladii ) the sexual process was 
very different from that observed in P. violaceum. In the aecidia of 
these forms fusion in pairs takes place between the uninucleate fertile 
cells ; cells with conjugate nuclei are thus produced, which then undergo 
a series of rapid divisions and produce the aecidiospores in the usual way. 
We have been able to confirm the existence of this type of fusion 
in the aecidium of one form which we investigated, and there is no 
doubt that it must be given equal rank with nuclear migration as a method 
of aecidium development ; but we are not able to accept Christman/s 
interpretation of his results. He looks upon the process he observed 
as a mere conjugation of undifferentiated gametes ; and though he comments 
on two such different types of sexual development occurring in the same 
genus, Phragmidium > he makes no attempt to bring them into line. 
If, however, the view be accepted that the fertile cells of P. vio- 
laceum represent female gametes, which are now fertilized by vegetative 
cells instead of by male cells (the now functionless spermatia), it fol- 
lows that the cells which fuse in P. speciosum — since the structure and 
development of the aecidium is exactly the same in the two cases — also 
represent female cells , which now conjugate in pairs. By such a very 
simple interpretation the two processes are reduced to a common term. 
The two species of Phragmidium are then seen to exhibit merely two 
different methods of dealing with the same problem — fertilization in the 
absence of the male cell. In the one case the male cell is replaced by 
a vegetative cell, in the other by another female cell. 
If, on the other hand, Christman’s view of the behaviour of P. 
speciosum be accepted, it must also apply to P. violaceum , and it 
leads to the unsatisfactory conclusion that the fertile cells here also 
represent undifferentiated gametes, which for some obscure reason have 
given up fusing in pairs, and now fuse with vegetative cells instead. 
The view put forward above obviously explains the relation of the 
two processes throughout the group, and has the further advantage of 
giving a reasonable explanation of the structure and occurrence of the 
spermatia, which in Christman’s view are left out of account. 
That the conjugation of female gametes may take place in the absence 
of the appropriate male cells is shown clearly by the authors’ studies 
on Humaria gramdata (2), where, in the absence of the antheridium, 
the female nuclei of the ascogonium fuse in pairs. 
The forms investigated were Uromyces Poa£ , Raben., Puccinia Poarum , 
Niels, and Melampsora Rostrupi, Wagn., for the development of the aecidia, 
and Puccinia Malvacearum , Mont., Puccinia Adoxae , DC., Uromyces 
Ficariae , Lev., and Uromyces Scillarum , Wint. 
