lO Wilson — Ol)scrvatio)is 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 Mntil 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. i). 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- 



