Nuclear Divisions in the Rusts. 
333 
a reduction of the cytoplasmic portion of the cell, but leaves the nuclei 
unchanged. 
Each female reproductive organ, according to Blackman’s conception, 
consists of a female cell below and a sterile cell above. He suggests that 
the sterile cell probably once pushed its way through the epidermis to the 
surface, and there functioned as a trichogyne, fusing with the spermatium. 
The vegetative nuclei migrate into the female cell either from the cell 
immediately below the female cell, in the same cell row, or from one of the 
smaller neighbouring cells at its base. The migration takes place, accord- 
ing to him, through a very small pore, that neither before nor after the 
passage of the nucleus could be distinguished. Whether any protoplasm 
passes over with the migrating nucleus Blackman could not determine. 
Christman (’05), working with Caeoma nitens , Uromyces Caladii , and 
Phragmidium speciosum , described a process of true fertilization by the 
fusion of two cells, which he regarded as decidedly different from Blackman’s 
method of nuclear migration. The two cells which fuse are of approxi- 
mately equal size, as are also their nuclei. Both cells may, according to 
Christman, cut off sterile cells before becoming gametes. The fusing cells 
are figured as lying side by side, and a considerable portion of the walls 
in contact dissolve away, so that the product of the union is a distinct 
double cell, composed of the cytoplasm and nuclei from the two equal 
gametes. In harmony with this account, the row of spores formed from 
the growth of this fusion cell is regularly borne on two cells forming 
a double base. Blackman’s basal cell, on the other hand, is really but one 
cell, with two nuclei. The latter contends that Christman’s fusion occurs 
between two ‘female cells’. Christman himself regards the fusion as rather 
of the nature of the conjugation of equal gametes, resulting in a non-resting 
zygospore. 
Blackman and Fraser (’06), in their further studies on the sexuality 
of the Rusts, have investigated seven additional species, three for the 
development of the aecidia, three micro-i orms, and one leptodoxm. Nuclear 
migrations were found to be the means for the initiation of the binucleated 
condition in the aecidium cups of Uromyces Poae and Puccinia Poarum . 
In Melampsora Rostrupi , a caeoma form without pseudoperidium, the 
authors found indications of a conjugation of two equal cells, in the same 
manner as Christman described. They therefore now give equal rank to 
nuclear migration, or ‘ partial cell fusion ’, as they term it (p. 44 ), and fusion 
of two equal cells, as the mode of origin of the binucleated condition in 
the group. 
Although convincing evidence was not obtained as to the method 
of transition from uninucleated to binucleated cells in the other four forms 
studied, the authors regard it as established that in the lepto- form, Puccinia 
malvacearum , the change to a conjugate condition takes place just before 
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