484 SECTIONAL TRANSACTIONS.—K. ee 
long periods. Other viruses and host plants were used primarily to confirm the results 
obtained with Aucuba Mosaic in Tomato. 
The movement of the agent about the host plant after inoculation was studied. 
When inoculation is made on any one leaf the symptoms of disease appear systemically, 
there being no localisation of symptoms about the region or side of inoculation. When 
a band of tissue half-way up the stem is killed so that only the xylem system remains 
functional, infection may be induced either above or below the lesion, but the agent 
will not pass from one part of the plant to the other when inoculation is made in only 
one part. 
niin juice may, however, be introduced through a cut petiole directly into the 
xylem vessels, and can travel freely in the water stream. On the other hand, the 
agent is apparently unable to leave the vessels in which it has travelled to infect the 
living cells of the plant. When the vessels are ruptured and their contents brought 
into association with the living cells of the mesophyll infection takes place. In the 
diseased plant the agent does not normally enter the xylem vessels, and is not found 
in the water stream or in the hydathode exudate. 
The evidence available suggests that the agent does not normally enter an unbroken 
cell, and that rupture of the wall and of the protoplast is necessary. On the other 
hand, if too extensive damage be done, or if the inoculum be slightly toxic, numbers — 
of cells are killed round the point of inoculation and the agent is unable to enter the — 
living cells of the leaf. It would appear that movement from cell to cell in the plant 
along the protoplasmic strands is fairly easy. The removal of a large proportion of 
the vascular tissue does not retard the upward movement of the agent. Further, 
the rates of movement of the agent up or down the plant from the point of infection 
appear to be the same. There is no evidence of a tendency to greater movement in 
either direction. | 
The general effect of the disease on the metabolism of the plant has been studied. — 
The rate of respiration has been selected as a criterion of general activity. The rate 
is being determined for diseased as against normal tissue. It has been found that, 
while virus disease considerably alters the appearance of the host plant—especially — 
as regards Aucuba Mosaic in Tomato—the stage of development is apparently not © 
affected. That is to say, the diseased plant is as fully developed at any given time 
as is the healthy control. ¥ 
Dr. H. G. Toornton.—The Influence of the Host Plant in Controlling the 
Formation and Functioning of Root Nodules in the Lequminose. 
Miss M. D. Grynne.—Infection by Synchytrium endobioticum of Potato 
Varieties previously considered immune. 
Varieties of potato which appeared immune to wart disease in the field were 
formerly supposed to be absolutely immune, showing no trace of susceptibility under 
any conditions. More intense methods of infection have, however, shown that among ~ 
these varieties are a considerable number in which incipient infections appear, but do 
not develop into true warts. They tend to disappear as the plant grows. A 
microscopic study of incipient warts shows that the parasite reaches different stages 
in different immune varieties and may produce ripe summer sporangia and much 
more rarely winter sporangia. Necrotic areas are found frequently in the neigh- 
bourhood of the parasite by means of which it is possible that the plant sloughs off 
the parasite or reduces the virulence of its attack. ‘ 
Mr. R. H. Sroucuton.—On the Cytology of Bacterial Plant Parasites. 
There are two distinct but allied problems in bacterial cytology and morphology. 
First, do bacteria possess a true nucleus comparable with that of all other known 
living cells; second, have bacteria any means of reproduction other than simple 
transverse fission and endospore production, and if so, what cytological changes are 
involved in the formation of these reproductive bodies ? Both of these problems 
have been attacked in the present work, carried out mainly on Bacterium malvacearum, 
the cause of a serious disease of the cotton plant, but extended té¥include certain 
observations on various other plant-pathogenic bacteria. 
