Oct. 1, 1925 
Telial Sorus in the Pine Rust 
647 
cleated cells at the base of the sorus by means of a granular aggrega¬ 
tion of decomposition products (fig. 1, I) stretched out so that it 
simulates the expandea stalk of a spore of Gymnosporangium. At 
different levels on all sides, uninucleated spores are still present (pi. 2, 
C). Such a picture is misleading, for it suggests that all of the spores 
are at first sessile, but that by a stretching of the basal part, and as 
a result of lateral pressures, the spores are brought to different levels. 
The spores developed at the margin of the sorus are greatly de¬ 
formed and truncated (pi. 1, C). Thpugh the terminal ones do 
germinate to form their internal basidia (fig. 1, H) they can be 
brought out into the open only by the great elongation of the spore 
below. Cross walls are not always laid down at right angles to the 
spore axis. This gives the spore cells the appearance of budding out 
at the side (fig. 1, G), especially if the wall of the spore above sepa¬ 
rates from the spore contents and undergoes mucilaginous dis¬ 
organization. 
Each cell of the internal promycelium has a single nucleus. One 
occasionally finds what might be taken to be two nuclei in each cell 
(fig. 1, M, N). One of the bodies, which is clearly a nucleus, is 
larger than the other. The smaller body seems to be more uniform 
in its composition, and stains less like a nucleus. Good fixation of 
these stages was not obtained. Binucleated sporidia are often found 
in the rusts, and it is possible that the original nucleus of the basidial 
cell sometimes divides precociously instead of waiting until it has 
passed up into the sporidium. 
DISCUSSION 
The amount of sterile tissue which is found overlying the sporog- 
enous cells in a rust sorus may not now depend altogether on the 
depth at which the primordium develops, but it is generally conceded 
that the location of a sorus with respect to the host tissues did, 
in evolution, have a considerable influence in determining the type 
of primordium evolved. Arthur (2) and others early recognized the 
importance of this feature. In some forms of deep-seated aecidia, 
the primordium is composed of a mass of intertwined hyphae without 
orientation. The host tissues are crowded aside and, by subsequent 
disorganization of the fungus tissue at the center, a cavity is developed 
and food made available for the growth of spores. Where a resistant 
host tissue above is to be ruptured, one may find that the sorus 
primordium is composed of a palisade arrangement of hyphal cells 
thrust against the tissue to be broken away. 
Had Lindfors (13) studied the organization of the telial sorus in 
Gymnosporangium and Cronartium and the uredinium in Puccini- 
astrum and Cronartium, or the deep-seated aecidia in certain Peri- 
dermiums, he would no doubt have anticipated the objections that 
have been raised against the theory that the sterile cells above the 
fusing cells are the morphological representatives of ancestral red- 
alga trichogynes, a theory which the propounder himself would no 
longer support. The nature of the sterile tissue lying above the 
fertile or fusing cells in a sorus is best understood, not by limiting 
one’s studies of rusts to cell fusions, but by also investigating those 
sori where no fusions occur. Colley’s method of study (If) of the 
white-pine blister rust, Cronartium ribicola , is to be commended 
particularly on this account. 
