212 
Journal of Agricultural Research 
Vol. XXV, No. s 
Rubus canadensis , mountain blackberry, from Bartlett, N. H., infected 
with the long-cycled Gymnoconia show that the gametophytic mycelium 
of this rust spreads through the root runners in the same manner as 
that of the short-cycled form. 
MYCELIUM IN THE DEWBERRY 
The rusl spreads in the wild dewberries in a totally different way. 
The trailing vines of the dewberry take root at the nodes or at the tips, 
and the mycelium in an infected plant, though confined to the pith in 
the differentiated region of the vine, fellows the growing point and enters 
the buds as they are formed, so that new plants originating at these 
rooting nodes are infected from the beginning. Hyphae are present in 
that part of the stem which is buried in the soil, and, contrary to what 
might be expected, there is considerable extension of the mycelium in 
the root system. Sections of a dewberry infected with the short-cycled 
rust showed mycelium in the roots for a length of at least 8 to io inches. 
The course of the mycelium was also followed in the root system of 
a wild dewberry infected with the long-cycled rust. No mycelium was 
found in the innermost wood ring. Hyphae were abundant in the tis¬ 
sues of the other rings, especially along the rays. The haustoria are 
often provided with short, more or less twisted and intertwined branches; 
in this case they are composed of several cells, each cell with a single 
nucleus. Such complex haustoria are more in the nature of intracellular 
hyphae, and nearly fill the cell attacked. The hyphae branch out in all 
directions on reaching the cambium and sieve tubes. Longitudinal sec¬ 
tions show that the parasite advances toward the tip of the root along 
the cambium and phloem, certain hyphae growing out radially as the 
root increases in size. The presence of mycelium throughout the woody 
tissues of these roots does not mean that the fungus can invade the 
wood, once the xylem is laid down. Hyphae originally present along 
the inner side of the cambium layer are simply cut off, or surrounded, 
by new wood cells. The mycelium now forms an intricate network by 
which hyphae in the phloem and the living medullary rays are in direct 
connection with that part of the mycelium in the wood, so that it is not 
surprising to find hyphae fully alive embedded in the wood of old roots. 
Passing from the primary to the secondary and tertiary roots, the my¬ 
celium is more and more confined to the outer part of the wood cylinder 
and phloem, until in the smaller rootlets i year old the writer found 
hyphae only in the soft tissue outside of the wood cylinder—that is, 
along the cambium, phloem, and in the cortical parenchyma—indicat¬ 
ing that practically all forward growth of the fungus takes place in the 
latter tissues. Certain roots of an infected plant may escape invasion 
by mycelium, and rust-free vines in such hills are not rare. 
MYCEUUM IN BEACK RASPBERRY 
Theoretically, the habit of the black raspberry cane which enables it 
to develop into a stolon which roots at the tip ought to serve admirably 
for the distribution of the long-cycled rust to new plants. In order to 
learn whether this were true, several rusted wild black raspberries have 
been marked and observed for three years. Not infrequently the rusted 
plants are so severely attacked as to die the second or third year. Again, 
the canes in the infected plants are of the witch’s broom type and they 
