10 Wilson—Observations on 
showing that it now had no organic connection with the rest 
of the oak, and this in spite of the fact that there can be no 
doubt that its centre was once a part of the oak root. 
It will be seen (Plate III) that these patches of scleren- 
chyma are found in the cortex of the oak root, that they 
gradually become larger and more numerous until finally 
they make up the bulk of the excrescence, and also that the 
diameter of the root increases in proportion to the amount of 
sclerenchyma present. 
Not only is the sclerenchyma continuous, but the “bark,” 
it will be noticed, covers, without apparent interruption, the 
root of the oak and the tubercles. 
The lines of invasion of the host by the parasite may be 
made out clearly in both of these plates, particularly if one 
looks carefully at the lower half. But in such natural speci- 
mens it would be difficult to understand the relationship of 
the parasite to the host, even with the most careful micro- 
scopic study. A study of the younger nodules, however, 
enables us to understand the larger growths. 
The youngest tubercle which I was able to find in the keg 
of material brought from Gallitzen was about half an inch in 
diameter, and growing at the end of a root fully three years 
old. The tips were already developed, tiny scales covering 
the rudiment of a flower stalk (Plate VI, Fig. 1). Figs. 2 and 
3 are drawings of tubercles of about the same size and appar- 
ent age. Fig. 2 has, however, more flower-stalk buds, which 
are farther developed in Fig. 3. In Fig. 2 is drawn a tubercle, 
beyond which the root still extends. The same thing will be 
noticed in Plate I. Nevertheless it was fairly unusual to find 
roots extending beyond even the younger tubercles. Like 
other parasites, it seems most frequently to prevent their 
growth and development, by cutting off and absorbing the 
nourishment originally intended for the younger parts of the 
root. 
Like the older tubercles, these were masses of scleren- 
