40 Blomfield and Schwartz—Observations on the Tumours on 
and it remains a stump-like pyramid bearing only dwarfed and deformed 
leaves, but where the invasion is less the growing point may free itself 
from the disease and leave behind a tumour on one side of the stem, 
causing it to twist or bend. It is this multiple origin of the tumour which 
gives to it the lobulated appearance seen in sections of mature tumours. 
We have failed to find any evidence of the wandering of the parasite from 
cell to cell, thus confirming Nawaschin’s opinion, expressed in his paper on 
Plasmodiophora, that the infected area is only increased by the division 
of already infected cells, and that neither the amoebae nor their nuclei 
have any power of penetrating through the cell wall into a healthy from 
an adjacent infected cell. 
We are of opinion that infection takes place in the neighbourhood of 
the growing point; this is the case when healthy plants growing in pots 
under observation are brought into contact with infected material. Though 
not having observed an actual infection, we have, as stated above, observed 
the infected areas getting smaller as we approach the growing point, and 
have seen single isolated infected cells close up to growing points; by 
repeated division of these isolated cells larger infected areas or groups of 
cells would be formed. 
Structure of the Tumour . The microscopical appearance of transverse 
sections of tumours varies, depending on how much of the stem has been 
involved in the early infection and on the stage of development of the 
parasite ; where there has been extensive infection of the tissues in the 
vicinity of the growing point the whole stem and leaf system is reduced 
to a pyramidal mass, in which the cortex, pith, &c., are not to be dis¬ 
tinguished, but in less extensive infections the tumour may involve only 
a portion of the stem and interfere but slightly with its growth, which may 
continue in the normal manner. 
The tumour consists of masses of infected and modified cells, sur¬ 
rounded by cambial cells showing here and there a few spiral and annular 
vessels. In a section of a slightly infected stem the tumour consists of 
a small infected area or group of cells situated in the cambial ring, showing 
in its earliest stage but little interference with the general structure of the 
stem, except perhaps a slight bulging due to mechanical pressure. 
The appearance of sections of tumours in various stages of develop¬ 
ment will be understood from Figs. 2, 3, and 4, which have all been drawn 
under a magnification of about 300 diameters by means of the camera 
lucida. These figures represent stages in the development of the tumour 
and parasite which may be fitly defined by the terms early, middle, 
and mature respectively. Fig. 2 shows a portion of an early tumour 
in longitudinal section ; on the right is the cortex, between which and the 
infected cells are to be seen some layers of cambial cells. The infected 
area itself is seen to consist of infected and modified cells, all of which 
