Generations, and General Cytology of the Uredineae . 355 
Poirault and Raciborski, the sporidium does become binucleate, but this 
appears to be a mere precocious division of the nucleus without wall- 
formation, for, as mentioned earlier (see under section dealing with sporidia- 
formation), the sporidia of Phrag . violaceum and a few other forms have been 
found to give origin, in spite of their binucleate nature, to the normal 
mycelium with single nuclei. Poirault and Raciborski, however, observing 
that the mycelium which gave origin to the uredospores and teleutospores 
had paired nuclei and that the sporidium also was binucleate, concluded that 
the former arose from the latter. They completely, however, overlooked 
the fact that C. Euphrasiae had been shown by Klebahn (26) to be 
a heteroecious form and that the sporidium really gave rise to the aecidial 
stage, the so-called Peridermium Pint , which in the case of C. Senecionis 
Sapin-Troufify had shown to have the typical structure, a mycelium with 
single nuclei. Holden and Harper (23) in a recent paper, observing that 
the sporidium becomes binucleate in a form to which they give the name of 
Coleosporium Sonchi-arvensis , Lev., have again put forward the view that the 
sporidium starts the stage with paired nuclei. Such a view, for the reasons 
just given, can hardly be accepted without direct evidence. The authors 
assume that the binucleated sporidium gives rise directly to the mycelium 
with paired nuclei which they investigated and found bearing the uredo- 
spores and teleutospores ; but it has been shown that the species in question, 
like that of C. Euphrasiae , is heteroecious (see Klebahn, 27), with its aecidial 
stage on Pinus , like nearly all the other species of the genus yet investigated. 
The aecidial stage in this form has therefore no doubt a mycelium with 
single nuclei like C. Senecionis and all the aecidial stages of the Uredineae 
hitherto known. The mere fact of the sporidium being binucleate cannot 
be considered as being of any special significance. It is true that the name 
C. Sonchi-arvensis has been applied loosely to a number of what are now 
known to be different forms, the original form being really confined to 
Sonchus in its second stage (see also Klebahn, 27). The Coleosporium on 
Aster and Callistephus will probably thus prove to be a new form, but there 
can be no reason to doubt its heteroecism, since nearly all the forms of the 
genus hitherto investigated appear to have two hosts. 
There is no evidence that the sporidium of any form ever gives rise to 
anything but a mycelium with single nuclei. As stated earlier, all the work 
of Sapin-Trouffy, of Maire, and that here detailed goes to show that the 
condition with paired nuclei always starts in the aecidium when that 
structure is present. Even in the absence of the aecidium the paired nuclei 
only arise later in the mycelium in connexion with the development of the 
uredospores or teleutospores 1 . 
1 Arthur (61), in reviewing the work on this subject, concludes that the sporidium regularly 
starts the condition of paired nuclei in the group, and is naturally at a loss to explain the fact that 
the spermatia are uninucleate. His views seem based on a misunderstanding of the work of Sapin- 
