Cc. A. BARBER. zal, 
and the small, upper portion only after secondary thickening 
has greatly added to the diameter of the haustorium. The 
collapsed layers in Santalwm, on the other hand, appear as' lines 
of pressure in the cortex when the nucleus begins to expand, 
little or no difference being observable in the cell contents on 
either side of them during their formation (Santalum, Part I, 
Plate V, figs. 22 and 31, and Part II, Plate I). 
As regards the vascular loop, there is thus far comparatively 
little change. In both this and the last stage, however, a 
horizontal plate of tracheides, divided in the middle line, has 
appeared immediately above the nuclear meristem (Plate V, fig. 
1, and Plate VI, fig. 1). 
12. No single instance has been observed among the 130 
haustoria examined in the preparation of this paper of one in 
the act of entering the root of the host. We are justified in 
supposing from this that, as in Santalum, the haustorium enters 
very quickly. The tissue behind the gland, consisting of an 
immense number of small active cells charged with protoplasm, 
has become greatly elongated as soon as a breach has been made 
in the host’s root. Profound changes in these tissues, chiefly 
due to the extension of the cells, have taken place in the act 
of entering, and it is, in most cases, difficult to trace their relative 
positions before and after penetration. The only method that 
has suggested itself of determining the extent of these changes 
is to select a haustorium which has entered some soft root or 
part of root and has thus been less distorted under the entering 
pressure, also which, by certain signs, as for instance the traces 
of a former gland, is seen to be in a youthful condition, and to 
compare it with that figured on Plate VI. This method has 
served to throw a good deal of light on the subject, as will be 
seen from figure 1 on Plate WII, where a young haustorium 
has penetrated a root of Asparagus racemosus but has as yet been 
unable to rupture the vascular cylinder, has not been cut off 
from the host’s cortex by bands of cork and has a distinct trace 
of a former gland, all signs of comparatively recent entry. 
