40 
Blackman and Fraser . — Further Studies on the 
PUCCINIA POARUM, Niels. 
The spermogonial and aecidial stages of this heteroecious form are 
found on the leaves of Tussilago Farfara , the aecidia appearing as round 
whitish swellings in their very young state. P. Poarum is peculiar in 
having two crops of aecidiae in each year, one in the spring and one in 
the autumn ; also two crops of uredospores and teleutospores arising from 
the aecidiospores. The material here investigated was obtained in early 
September. 
The aecidia arise somewhat deeper in the leaf tissue than in the case 
of Uromyces Poae , but their general development is very similar. The 
fertile cells arise in the same way, though their early stages are even more 
irregular, and there is the same doubt as to the presence, or absence, of 
definite sterile cells. 
Nuclear migrations (Figs. 12 and 13) of the usual type were observed 
in connexion with the differentiated fertile cells. It was noticed, however, 
that paired nuclei were also to be observed at a stage before the differentia- 
tion of the fertile layer, or in cells below that layer after its differentiation. 
This suggested that nuclear migrations might sometimes take place in cells 
which had not yet differentiated into fertile cells. This view proved to be 
justified ; for besides the ordinary nuclear migrations mentioned above, one 
case was observed of a nuclear migration from one vegetative cell to 
another (Fig. 14). The cell so fertilized was just below the layer of fertile 
cells, and presumably it would either grow up directly into a fertile cell, or 
it might divide further before giving origin to the definite fertile cells. 
We thus have in P. Poarum two types of nuclear migration in con- 
nexion with the development of the aecidium : one an ordinary nuclear 
migration (reduced fertilization) into a fertile (female) cell, the other a less 
common process, in which a vegetative cell is fertilized in a similar way, 
and later gives origin to a fertile cell or cells. The latter process is of 
great interest, for when it occurs the homologue of the female cell is 
actually fertilized from its very origin. It is as if the prothallial vegetative 
cells investigated by Farmer, Moore, and Digby ( 5 ) should, after fusing, 
produce an oospore (containing naturally the double number of chromo- 
somes) from which the embryo arose later. 
This form also was carefully examined for the fusion described in 
other cases by Christman ( 4 ), but no evidence of such a process could be 
obtained. 
The development of the spores and of the pseudoperidium is the same 
as that of Uromyces Poae . 
Cells with three and with four nuclei were observed in this form also, 
and a spore-mother-cell of each kind was seen in division (Figs. 15 and 16), 
showing clearly that in these abnormal cases there is true conjugate division. 
