of some Phanerogamic Parasites. 321 
the fibro-vascular bundle by the side of which it grows, and it 
pushes its apex deeper and deeper into the medullary ray, 
the cells of which contain much starch. 
In the same way, but less rapidly, the structure grows 
toward the surface of the root, pushing up the overlying 
cortical tissues. One side is applied to the phloem of the 
adjacent bundle. It is noticeable that the growth of this 
structure causes very few cells of the host to collapse. This is 
accounted for by the fact that, at first, it does little more than 
keep pace with the rapid growth of the whole root. Presently, 
however, that part of the now rather spindle-shaped mass of 
cells which lies beyond the cambium toward the periphery, 
begins to grow more rapidly. Thus the overlying tissues are 
compressed and pushed upward, forming the increasingly 
large hemispherical swelling on the surface of the root 
(see Fig. VI, PL XV). As already shown by Graf Solms x , the 
growth of the parenchymatous mass now becomes very slow, 
except at the outer end of the spindle. A definite growing- 
point is formed, from the sides of which the bracts and floral 
envelopes are successively cut off (see Fig. VI), while from its 
apex the stamens and pistil are later developed. 
Just before the first bracts appear, the differentiation of 
the first fibro-vascular bundles takes place, in a region several 
cell-layers from the sides of the now top-shaped mass of 
parenchyma, and about in a line with the older parts of the 
phloem of the adjacent bundles of the host. These young 
bundles originate, and remain, distinct from one another, their 
development taking place both upward as the bud grows, and 
downward toward the base of the bud. The bundles are very 
simple, collateral, open, composed of short tracheids and 
xylem-parenchyma, of several layers of cambium-cells, and of 
short phloem-elements. As the bundles develop, a direct 
union is effected between the tracheids and the adjacent 
xylem of the host, and the phloem unites, in similar fashion, 
with the phloem of the host. 
Only in buds well advanced in development is it possible to 
1 loc. cit. 
