Nuclear Divisions in the Rusis. 
347 
same cell are to be found in the next section of the series. Other cells 
round about the one here illustrated have resting nuclei which seem to 
be exceedingly well fixed (see, e. g. Fig. 25, in which fifteen such nuclei are 
shown in one cell), so that the peculiar appearance in this one cell can 
hardly be said to be due to poor fixation. Although I am not prepared to 
explain all the details of the mitosis for this form — Puccinia Cirsii-lanceo- 
lati — I am fairly certain that such stages as are here represented are early 
prophases. We have then presented in this instance the peculiar phe- 
nomenon of twelve nuclei in the one cell undergoing division at the same 
time. Further, the variously irregular positions assumed by the figures 
suggest that the paired, or conjugate, arrangement seen in the binucleated 
cells is here not at all maintained. 
A still more convincing case is shown in Fig. 24, from the basal region 
of the aecidium on Cicuta , in which the six nuclei here drawn (as well 
as three additional ones which lie in a lower plane) show clearly the 
prophases of division, as well as the fact that the spindles maintain no 
definite paired relation to each other. The various central spindles are 
oriented in such a heterogeneous fashion with respect to each other that it 
is difficult to imagine how, in these multiple divisions, there can be any 
maintenance of a conjugate relation. The principal point to be noted 
in this place, however, is the fact that where such multinucleated cells occur, 
the tendency is for the nuclei to divide simultaneously. But that this 
is not universal in such conditions is indicated by some apparent exceptions 
which I have found. While it is not the purpose of this paper to discuss 
the important questions which arise as to the origin of these multinucleated 
cells, and as to the part they take in the development of the aecidia, I wish 
merely to add the suggestion that the lack of evident pairing of the nuclei 
is probably comparable to the somewhat irregular relation seen in the 
young fusion cells of Triphragmium (Fig. 14), where the paired spindles 
may at first be variously oriented with respect to each other. It is, of 
course, possible that we have here multinucleated gametophytic cells, in 
which we should expect no pairing of the nuclei. But, although convincing 
evidence is as yet lacking, I am inclined to regard such cells as sporophytic 
in their origin, and as resulting from the greatly stimulated growth which 
follows sexual cell fusions. 
General Discussion. 
The conjugations by means of which the cells of the Rusts become 
changed from a uninucleated to a binucleated condition are certainly 
not to be associated with the simple anastomoses or fusions for nutritive 
purposes such as occur in the hyphae of many fungi. As Maire, Blackman, 
and Christman agree, this step in the Rusts marks the beginning of the 
binucleated condition of the sporophyte generation. The uninucleated 
B b 
