324 Blackman. — On the Fertilization , Alternation of 
are nothing more than accessory asexual reproductive organs to which the 
terms pycnidia and conidia should more aptly be applied. These ideas 
were followed by Van Tieghem (54) and by Vuillemin, and have of late 
years gained considerable acceptance 1 . 
The great objection, however, to the view that the spermatia are of 
conidial nature is that they seem quite incapable of causing infection ; the 
fact that they appear about the same time as the aecidiospores is also an 
argument against this view, as will be shown later. 
Although it is clear that a careful cytological study would most likely 
throw great light on the vexed question of sexuality in this group, yet 
for a very long time our knowledge of the cell structure of the Uredineae 
was confined to a few scattered observations by Schmitz (49) and Rosen (45). 
About ten years ago, however, the researches of Poirault and Radiborski (43) 
and of Sapin-Trouffy (48), a pupil of Dangeard’s, threw very considerable 
light on the cytology of this group. The former observers showed that 
in many stages of the Uredineae the nuclei were to be found closely 
associated and dividing in pairs (the conjugate nuclei of these authors), each 
pair in a separate cell. Sapin-Trouffy carried the matter further, and 
showed that the following very interesting cycle of nuclear development 
was to be observed in the forms possessing an aecidium (Eu- and -opsis 
forms). The mature teleutospore is always uninucleate and gives origin to 
four uninucleate sporidia from which a mycelium arises in which the nuclei 
are arranged singly, usually in separate cells. In the aecidium, borne by 
this mycelium, the nuclei, however, become paired ; the aecidiospores thus 
contain two nuclei, and the paired condition of the nuclei is retained 
throughout ensuing mycelia and uredospores (if present) up to the teleuto- 
spores, which in the young state are binucleate, but at maturity become 
uninucleate by the fusion of their nuclei. In all cases of division of the 
paired nuclei the two are very closely associated, and a half of each nucleus 
goes to the new cell, so that the two nuclei in the cells produced by division 
are never daughter-nuclei. 
These very striking observations throw no light on the nature of the 
spermatia, for though the latter were shown to be uninucleate, like the cells 
of the mycelium on which they are borne, Sapin-Trouffy assumed their 
conidial nature and paid little attention to them. For him the most 
important stage in the cycle just described was the fusion of nuclei in the 
teleutospore, a fusion which he considered to be of the nature of a true sexual 
process 2 , and to be comparable with the fusion in the ascus and in the 
basidium. On the facts observed, however, there does not seem sufficient 
evidence for such a view ; for a process of fusion which takes place in a cell 
1 A full account of the older observations on the nature of the spermatia and the sexuality of 
the group is given by Klebahn ( 27 , pp* 194-202). 
2 Dangeard and Sapin-Trouffy ( 18 ) had earlier considered it as a ‘ pseudofecondation.’ 
