356 Blackman. — On the Fertilization , Alternation of 
NUCLEAR DIVISION. 
From the observations of Poirault and Raciborski, Sapin-Trouffy, and 
Maire- — although they did not observe all the details of the process and their 
interpretation is clearly at fault — there can be no doubt that the type of 
nuclear division here described, whether for single or conjugate nuclei, 
is general for all the Uredineae. It is clear then that in all of the divisions 
in the group, except those in the promycelium, we have to deal with 
a process of such a simple nature that chromosome-formation is in complete 
abeyance ; so that the division actually partakes of the nature of direct 
division (amitosis). A comparison, in such a form as G. clavariaeforme , of 
the first and second divisions in the promycelium with the other simple 
divisions (whether single or conjugate), leaves no escape, however, from 
the view that the simple method of division is really a reduced form of 
indirect division. The first promycelial division is a fairly typical form of 
mitosis with a formation of chromosomes, though the absence of any 
regular equatorial plate, the fact that no splitting can be observed, and the 
early fusion of the chromosomes suggest that perhaps even here the process 
may be reduced from a halving of definite chromatin elements to the more 
or less direct separation of chromatin material as a whole. In the second 
division, however, though the spindle structure is perfectly typical, the 
chromatin instead of forming distinct chromosomes merely forms a network 
which becomes spread out on the spindle and later draws apart into two 
portions 1 . If this second method of division be still further reduced, so 
that the chromatin instead of forming a network forms a solid mass and 
the spindle is represented only by a fine, thread-like structure, we have the 
ordinary method of division characteristic of the nuclei, whether single 2 or 
paired, of the cells other than those of the promycelium. 
It seems impossible to doubt that these three methods of division 
represent progressive stages in a process of reduction, for it is hardly 
Trouffy, who showed clearly (and his work has been confirmed by Maire and in this paper) that the 
spermogonium was always borne on a mycelium with single nuclei. Arthur also states that it has 
been shown that both aecidiospores and uredospores arise from a binucleated mycelium in the usual 
vegetative manner. This is directly contrary to the facts observed by Sapin-Trouffy eight years ago, 
who in all cases found that the aecidiospores were borne on a mycelium with single nuclei, and 
that the nuclei only became paired at the time of aecidium-formation. 
1 Whether the two promycelial divisions are regularly different in other forms as in G. clavariae- 
forme remains for future work to show. Holden and Harper (23), in their recent paper, are of the 
opinion that in the species of Coleosporium which they examined the two divisions are of like nature, 
though they were not fortunate enough to have such a complete series of stages as were obtained for the 
form here investigated. 
3 In the divisions of the single nuclei, as observed in the spermatial hyphae, the spindle 
structure is not so clear. A precocious division of the nucleus of one of the four 1 promycelial ’ cells 
has been observed, however (while this paper was in the press), in G. clavariaeforme , which shows 
a distinct spindle, though without centrosomes or polar radiations (Fig. ioo). This shows that the 
achromatic part of the nucleus may not always be as reduced as in most of the divisions observed. 
