J une z6, 1923 
Pucciniastrum americanum 
893 
and Rees, as noted, state that the uredospores of Pucciniastrum agri- 
moniae are borne in chains and that the terminal cells of the chains 
elongate to become the peridial cells, the other cells developing one by 
one into uredospores as described by Magnus for Melampsorella. These 
authors did not find intercalary cells either in the spore chains or below 
the peridial cells. If this were true, the peridium would be formed in a 
manner analogous to that of the aecidium, as they pointed out. 
Some of the strongest hints as to the trend in evolution are suggested 
by what it is thought are atypical processes; but if in addition to the 
method of spore formation which the author has observed in Pucciniastrum 
it should be rarely found that every cell below the peridium in the cell 
chains develops into a uredospore, as claimed by Ludwig and Rees, the 
doctrine of homologies would be weakened. The bufer cell in the 
telium of Gymnosporangium may be the homolog of the peridial cell in 
Puccinastrum; this depends on just how the first intercalary cell in the 
latter is cut off. It is not the homolog of the peridial cell of the ordinary 
aecidium, but rather it is comparable to the hymenial basal cell or its 
sister peridial initial. If the uredospores of Melampsorella cerastii are 
always borne in chains, and those of Hyalopsora are borne singly on 
pedicels, then the species of Pucciniastrum form a good series of con¬ 
necting links, P. hydrangeae being more nearly like Melampsorella, 
especially if we should find intercalary cells in the latter. 
The complete life history of P. americanum is unknown. Three other 
species of the genus have their aecial stage on Tsuga and two on Abies. 
The occurrence of our rust on canes of the current season suggests that 
the fungus may live through the winter, thus obviating the necessity 
for the alternate aecial stage in certain localities. No explanation has 
been offered to account for the presence of the deep-seated, inverted sori 
on canes, which are very common. It is possible that the inversion may 
facilitate spore discharge the following spring as the cortical parenchyma 
peels off, exposing the cork tissue below. Such inverted sori were not 
found on leaves or petioles. 
It has been shown that the form and size of sori vary greatly, depending 
upon what tissue they are found, indicating that P. arcticum and P. 
americanum are not distinct species. In the event that it can be shown 
that Rubus triflorus and R. arcticus can not be infected with spores from 
R. strigosus and related forms, distinct names for the strains or biologic 
forms might still be desirable. 
LITERATURE CITED 
(1) Arthur, Joseph Charles. 
1920. NEW SP^ciBS OP urKdinKak-xii. In Bui. Torrey Bot. Club, v. 47, p. 465- 
480. 
(2) - 
1922. new species OP uredinEae-xiv. In Bui. Torrey Bot. Club, v. 49, p. 
189-196. 
(3) Bartholomew, E. T. 
1916. observations on the pern rust hyalopsora polypodii. In Bui. 
Torrey Bot. Club, v. 43 > P- i 95 ~i 99 -* 3 fig- 
(4) Christman, A. H. 
1907. THE alternation OP GENERATIONS AND THE MORPHOLOGY OP THE SPORE 
PORMS IN THE rusts. In Bot. Gaz., v. 44, p. 81-101, pi. 7. Literature 
cited, p. 99-100. 
(5) Davis, J. J. 
1921. [pucciniastrum.] In Mycologia, v. 13, p. 58. 
( 6 ) 
1922. [pucciniastrum.] In Mycologia, v. 14, p. 46. 
