220 BROWN. 
may be entirely within that of the host. After the separation 
of the apical region from the host the parasite grows con- 
siderably before it breaks through the bark. This is accom- 
panied by a considerable stretching of both host and parasite. 
The cambium of the parasite has comparatively little to do with 
the growth of the shoot. It would appear that all of the tissues, 
except the vascular elements, remain more or less meristematic 
until a very late stage and that growth and division take place in 
all parts of the shoot. The result is that there is a considerable 
enlargement of all parts, except perhaps the tip of the base. 
Figure 23, which is from a cross section of the central part of a 
young bud, shows divisions taking place in all directions. 
While the above-mentioned processes are going on, a phel- 
logen layer is differentiated in the outer layers of that part of 
the bark of the host which surrounds the parasite. As the 
parasite develops, this phellogen layer continues to produce new 
cells while the older ones on the outside become stretched and 
tend to be separated by cracks. This results in giving the bark 
a rough appearance, which becomes more prominent as devel- 
opment proceeds. 
As the parasite continues to grow, the flower bud, which has 
become separated from the bark of the host, finally breaks 
through it (figs. 6-8). The bark of the host, however, remains 
attached to the stalk of the parasite until a very late stage when 
it may become separated in places by the activity of the phel- 
logen-like layers to be described later. The first sign of the 
breaking through of the flower bud is the appearance of a crack 
in the bark of the host across the top of the swelling (fig. 6). 
This gradually increased in length and other intersecting ones 
make their appearance. The flower bud, which is continually 
enlarging, then grows out through the opening made by these 
cracks (figs. 7, 8). The formation of the cracks is evidently 
due to pressure exerted by the turgid, growing bud. 
MacDougal," while experimenting with artificially produced 
parasites, found that one plant could not be made to grow upon 
another unless the juices of the graft had a higher osmotic pres- 
sure than those of the stock. Judging from the great turgid- 
ity of the cells of Rafflesia manillana, it would seem that their 
contents must have a higher osmotic pressure than the contents 
of those of the root. The ability of the parasite to grow in the 
" MacDougal, D. J., and Cannon, W. A., The Conditions of Parasitism in 
Plants. Carnegie Institution of Washington. Publ. 129 (1910). 
