Generations , and General Cytology of the Uredineae . 353 
means of the spermatia has been replaced by a fertilisation of the female cell 
by the nucleus of an ordinary vegetative cell. 
Such a view receives strong support from the observation of Farmer, 
Moore, and Digby (14) on apogamy in Ferns, published while this work 
was in progress. There seems no doubt that the process in the aecidium 
is to be looked upon as intermediate between that of normal fertilization, 
where both the cells are specially differentiated, and that observed in 
apogamous Ferns by these observers, where both acting male and female 
cells are represented by ordinary vegetative cells. 
If the view be accepted that the process observed is a reduced form of 
ordinary fertilization, it seems very probable that the sterile cell also is 
reduced. Its position above the fertile cell would suggest that it formerly 
acted as a receptive cell pushing up between the epidermal cells as a 
trichogyne to which the sticky spermatia could be brought, for example, 
by insects. Some support is lent to such a view by the fact that occa- 
sionally cases are to be found in which the sterile cells do push up 
between the epidermal cells and swell out above, being merely covered 
by the cuticle (Fig. 77 a). If development were pushed one stage further 
and the cuticle pierced, a very effective receptive organ would be the 
result. 
MORPHOLOGY OF THE AECIDIUM. 
Although this subject cannot be treated fully in the absence of a 
comparative study of aecidium development in various members of the 
group, yet, as has been stated earlier, the aecidium of Phragmidium (and 
apparently that of Caeoma) is very different from the typical aecidium found 
in the other genera. It is merely a group of special reproductive organs, 
indefinite in extent, and merely bounded by paraphyses which are some- 
times absent ; and thus no more a definite structure than the sorus of 
uredospores or teleutospores. 
In the light of our present knowledge the aecidium of Phrag. violaceum 
is thus to be considered as a group or sorus of female reproductive organs , 
each consisting of a female (fertile) cell below and a sterile cell above. 
We probably have in this genus the most primitive form of the aecidium 
to be found in the group, but of the form of the aecidium in the still more 
primitive state when fertilization by the spermatia yet occurred, we can say 
nothing 1 . With the change to the reduced form of fertilization, with its 
obvious advantage of certainty, the number of female organs in the group 
could be indefinitely extended without the necessity of breaking through to 
1 It is of course possible that the spermatia may sometimes really act as fertilizing agents in 
Phragmidium , and perhaps in Caeoma , for they are occasionally found scattered over the surface of 
the leaf below which the aecidium is developing ; and if a sterile cell should push through to the 
surface and come in contact with a spermatium fertilization might result : such a process, however, 
was never observed, and it can only be of very rare occurrence. 
