498 
Journal of Agricultural Research 
Vol. XXV, No. i% 
esting to note that soon after the period is reached in a vigorous blackberry 
shoot when mature aecidia appear with the unfolding of the leaf, the tip of 
the new cane begins to outstrip the parasite in the upward growth, and the 
production of aecidia ceases; the grower says, “ the plant is recovering. ” 
That it is the gametophytic mycelium and not the sporophytic that has 
the power of inducing this morphological change in the host leaf is clear 
from a comparison of two sets of leaves, each bearing teleutosori. One 
collection was made July io at Lakewood, N. H. The leaves were thickly 
covered with spermogonia accompanied by an abundance of teleutosori, 
the aecidial stage having been suppressed. There were about the same 
number of stomata on both sides of the leaf. The other collection was 
made September 6 in Maine; these leaves, of course, bore only teleuto- 
spores. There were no stomata on the upper, side, while the lower side 
was provided with what seemed to be the normal number. The occur¬ 
rence of stomata on the upper side of leaves bearing spermogonia or aeci¬ 
dia could no doubt account for the infection of these leaves by aecidio- 
spores. The two sorts of mycelium, systemic gametophytic and local 
sporophytic, not being antagonistic, develop their own reproductive 
bodies, spermogonia and teleutospores, side by side. 
It has frequently come to the writer’s attention that some of the earliest 
and most abundant development of teleutospores has occurred on leaves of 
old canes. These leaves must have been fully formed by the time aecidio- 
spores were shed; this is especially true of systemically infected plants. 
Mountain blackberries harboring the orange-rust were transplanted from 
Maine to Maryland. In August, 1921, the leaves on the ‘hew” canes 
bore an abundance of teleutosori, the “old” canes were defoliated and 
dying at this time. Early in June of the following year practically every 
leaf on the old canes bore teleutospores. These plants were watched 
again in 1923. Teleutospores first appeared on leaves of old canes which 
had previously borne spermogonia and frequently also aecidia. The 
position of the leaf on the cane, whether at the tip or at the base, was 
clearly of no great importance. The leaves on the new canes remained 
free from the telial stage during the summer of 1922. All leaves on the 
old canes had unfolded at about the same time and had borne aecidia, 
and would have been equally susceptible so far as maturity is concerned. 
On the other hand, leaves develop on the new canes one by one, as previ¬ 
ously noted, so that as aecidiospores are shed leaves of different ages 
would be exposed. In this particular case in 1922 either the leaves on 
the new canes had not opened or they were not sufficiently mature when 
the spores were shed. 
After seeing that leaves harboring the gametophytic mycelium were 
provided with additional stomata on the upper side, it occurred to the 
writer that this might account for the production of telia on so many leaves 
of the old infected canes. Aecidiospores were sowed on the upper side 
of leaves bearing spermogonia, the leaves then being placed in damp 
chambers. After two days the leaves were dropped in Flemming’s 
fixture. The germ tube grows along the surface until it comes into the 
immediate vicinity of a stoma, then, if necessary, the end turns sharply, 
broadens out and sends the infection tube through the opening. The 
method of penetration was observed without sectioning by removing 
the chlorophyll from leaves killed in the Flemming’s fluid. There were 
in the greenhouse on April 18 a number of potted plants of Rtibus occi - 
dentalis systemically infected with the Gymnoconia, and now showing 
spermogonia. On many leaflets, especially on old canes, spermogonia 
