346 Blackman. — On the Fertilization , Alternation of 
In some cases, as in the case of the divisions of the single nuclei, it can 
clearly be observed that the chromatin does not form a single rod but a double 
rod (Fig. 96), which becomes drawn out into two pairs of chromatin masses, 
so that at this stage of the anaphase the nuclei show two opposite groups, 
consisting of four chromatin masses (Figs. 97 and 98). How far the 
presence of these two masses in the nucleus is of common occurrence it is 
difficult to say, for if the plane of separation of the two lies at right angles 
to the direction of view they would easily be overlooked. There would 
seem to be no doubt, however, that they are only occasionally present in 
the divisions in Phragmidium ; in the teleutospore in Gymnosporangium , 
however, the double chromatin mass seems to occur more frequently. 
It is the appearance of these two chromatin masses which led Sapin- 
Trouffy ( 48 ) and Maire ( 29 , 30 ) to the belief that the nuclei in the 
Uredineae possess in all cases two chromosomes, while Poirault and 
RaSiborski ( 43 ), observing the single mass, considered it to represent 
a single chromosome. It is obvious, however, that neither the origin nor 
behaviour of these structures is that of chromosomes, and the observation 
of numerous chromosomes, described earlier for the promycelial divisions, 
is sufficient to negative such a view. The real nature of these chromatin 
masses is, however, apparent on comparison of the divisions in the 
promycelium with the simpler divisions, either single or paired (conjugate), 
found in other stages of development. In both the promycelial divisions 
the chromatin (vide supra) shows at times a distinct segregation into two 
masses (Figs. 30, 32, 41 a). These masses are certainly not themselves 
chromosomes, and in the first division are clearly produced by the aggrega- 
tion of numerous chromosomes ; they probably represent, as suggested 
earlier, the chromatin derived respectively from the two nuclei which fuse 
in the teleutospore. It is not surprising then that nuclei which are the 
direct descendants of those in the promycelium should also show a similar 
tendency to a differentiation of their chromatin into two masses, though 
they have apparently ceased to form chromosomes. A comparison of 
Fig. 30 with Figs. 94 and 9 6 shows clearly the strong resemblance between 
the form taken by the chromatin in the two types of division. 
NATURE OF SPERMATIA. 
As the study of Phrag. violaceum clearly shows, the spermatia take no 
part in aecidium-development, and fertilization is regularly brought about 
in another way. This result is only in agreement with all earlier work, which 
has always failed to establish any direct relation between the spermatia and 
the aecidia. A fertilization of the fertile cells would obviously be difficult 
in Phragmidium, but it would be almost impossible in the typical aecidium, 
where the fertile cells are developed deeper down in the tissues. 
