sept. 16, i 9 i8 Tissue Invasion by Plasmodiophora brassicae 
557 
knobs. A section through one of these knoblike branch roots is shown 
in Plate 69, B. When such diseased branches arise from rather young 
roots, it sometimes happens that the diameter of the branch root is as 
great or even greater than the diameter of the root from which it arises. 
The disease also stimulates the production of buds in places where 
they do not normally occur. These buds often arise in great numbers 
from infected roots. This phenomenon was first observed by Woronin 
(i6). It has been somewhat more carefully studied by Favorski (4). 
The tissues of such buds are always infected. In most cases they grow 
into short fleshy shoots like that shown on a branch root in Plate 71, A. 
The leaves are thick, distorted, and abnormally succulent. In other cases 
the buds grow and give rise to sprouts of considerable size. Such sprouts 
may push above the surface of the ground and become green. An 
example is shown in Plate 71, B. The leaves of these large sprouts 
become green and appear quite normal. Sections through such leaves 
show that the parasite is more or less evenly distributed throughout 
their tissues. In some cases there is a tendency for the plasmodiu to be 
more abundant in the tissues bordering on the veins. A cross section 
through a diseased leaf is given in Plate 72, A. 
One interesting thing shown by the diseased buds is that they are 
often unable to respond normally to gravity. Sometimes they arise on 
the underside of a root and grow directly downward. In other cases they 
arise laterally and turn downward like the young sprout shown in Plate 
72, B. They have also been observed to grow out horizontally, but this 
is not so common as downward growth. 
The writer has studied the diseased buds with a view of determining 
whether or not the parasite is distributed in them by the numerous cell 
divisions that occur in the growing tip. This study has consisted in the 
observations of serial sections through a few of the diseased buds. The 
observations have not been extended enough to draw final conclusions, 
but the indications are that the parasite is not distributed to any great 
extent by cell divisions in the growing tip. Here, as in old roots and 
stems, its distribution is by means of direct penetration. The plasmodia 
follow closely behind the growing tip. Sometimes thay even infect some 
of the cells of this region. Most of the cells, however, have been found 
to be free of infection in the cases studied. The distribution of the para¬ 
site in these sprouts can not be accounted for by growing tip infection as 
Favorski (4) seems to have believed. 
HISTOLOGY OF THE CLUB 
Some attention should be given here to the response which the host 
tissues make to the attack of this enemy parasite and more especially to 
the pathological histology of diseased organs. This phase of the disease 
has scarcely been mentioned by previous workers. Perhaps the explana- 
