Jan. 1,1925 
Composite Life History of Puccinia podophylli ScJiw. 77 
Olive, the conjugate condition may be 
assumed to arise on the mycelium before 
the primordium of the sorus develops, 
or at least in a very early stage of its 
development. In connection with the 
sori on the sheaths, stems, and sepals, 
the change from a uniucleate to a 
binucleate condition would be expected 
to take place soon after infection, 
which would account for Olive having 
found uninucleate mycelium only in 
small amount. On the leaves, how¬ 
ever, the change would be expected to 
take place later, after the pycnia are 
formed, and hence, as Olive found to 
be the case, a considerable mass of 
uninucleate mycelium would be ex¬ 
pected. 
Once the binucleate condition has 
been established in the mycelium there 
are no difficulties from a cytological 
point of view as to the spore form 
produced, since both aeciospores and 
teliospores arise from binucleate cells. 
It is very likely that the type of spore 
produced is determined by the nutri¬ 
tional conditions prevailing in the host. 
However, it should be borne in mind 
that the tendency to an unstable con¬ 
dition is quite certainly inherent in 
the rust itself and the nutritional 
factors are best interpreted as second¬ 
ary, serving primarily to explain the 
situation as we find it and in view of 
our present, perhaps incomplete, cyto¬ 
logical knowledge. 
That telia are the first structures 
developed from infections on the 
sheaths, stems, and sepals is perhaps 
correlated with the influence of the 
rapid maturity of the tissues of these 
organs and the nature of the available 
nutrient. This influence was recog¬ 
nized by Olive. He used it, however, 
to explain why telia were formed 
instead of “secondary” aecia on the 
“perennial” sporophytic mycelium. 
The occurrence of telia in associa¬ 
tion with the aecia on the leaf blades, 
which has been repeatedly mentioned, 
is readily correlated with Olive’s cyto¬ 
logical observations and can best be 
explained also by the factor of food re¬ 
lations. Olive finds that the aecia are 
borne on a binucleate mycelium. It 
would appear quite logical to expect 
that this same mycelium might produce 
telia when the factors which determine 
teliospore production become opera¬ 
tive. 
The development of telia in associa¬ 
tion . with aecia usually occurs some¬ 
time after the majority of the aecia are 
mature. It would seem reasonable to 
suggest that the development of telia 
under these conditions may be due to 
the depletion of the local food supply 
by the mycelium during the develop¬ 
ment of the aecia and aeciospores, or 
directly to the more mature condition 
of the tissues. Perhaps, however, 
their formation is best explained by a 
combination of these two influences. 
In some cases the telia that develop in 
association with the aecia appear prac¬ 
tically simultaneously with them. This 
is especially true when the lesion in¬ 
volves the midrib or one of the larger 
veins. In such cases the explanation 
is similar to that given above to ac¬ 
count for the development of telia only 
on stems, sheaths, and sepals. The tis¬ 
sues of the veins and midrib are quite 
comparable in the character of the 
food supply to that of the stem. It 
has already been noted in the discus¬ 
sion of the life history that when ma¬ 
ture leaves are infected with basisio- 
spores, telia may predominate over the 
aecia in the resulting lesions and in 
rare cases may be formed exclusively. 
It has been repeatedly observed in 
connection with many long-cycle rusts, 
that as the hosts approach maturity 
there is a gradual reduction in the de¬ 
velopment of repeating spores and a 
corresponding increase in the develop¬ 
ment of the teliospores either in the 
same or separate sori. It would seem 
that this situation exactly parallels 
that in the Podophyllum rust except 
that since there are no repeating spores 
the teliospores developed in association 
with the aecia normally occur in sep¬ 
arate sori. As noted in the discussion 
of the life history, however, teliospores 
may rarely develop in the aecial cups. 
It is important to note, however, 
that only a few other cases have hitherto 
been observed where aecia have been 
replaced by telia. In most rusts the ma¬ 
turity of the tissues affects aeciospore 
production largely by reducing the 
number of aecia produced or the 
quantity of aeciospores. It has been 
repeatedly observed in the laboratory 
at La Fayette in connection with 
heteroecious culture work that when 
over-mature leaves or those in a poor 
growing condition are inoculated, while 
pycnia may be formed to some extent, 
few if any aecia develop. The fact 
that aeciospores are replaced by telio¬ 
spores in the Podophyllum rust is 
therefore another indication of the 
plastic and unstable condition of this 
species. 
The assumption that the conjugate 
condition arises at an early stage in 
the development of the mycelium can 
also be used to explain the fact that 
aecia may occasionally be developed 
without the pycnia. In such cases 
the change may have taken place 
