12 Wilson—Obdservaiions on 
are present. Now, it is perfectly conceivable that the irrita- 
tion to the oak caused by the continued downward growth of 
the parasite would have the effect of hastening the formation 
of the sclerenchyma, thus effectually resisting further attack 
of the parasite, which would then perforce penetrate more and 
more deeply into the oak with the same result of scleren- 
chyma formation following its progress. 
In this connection, the drawings in Plate VI, Figs. 1 and 2, 
are most suggestive. The root of the oak actually rises up 
to meet the parasite. In the vertical section (Plate V, Fig. 5), 
its solid tissue spreads outward and upwards into the softer 
tissue above. 
Plates I, I] and III can now be understood. Each of the three 
tubercles in Plate Iis the growth ofa single seedling. The differ- 
ence in size is the consequence of the varying age of the para- 
sitic mass. These tubercles are partly the result of the growth 
of the host, due toirritation of its tissue. This growth of the 
host is shown in the swollen appearance of the root, just below 
as well as in the base of the tubercle, and also in the masses 
of sclerenchyma which make up the greater part of each 
tubercle. The parasite proper consists of the flowering stalks 
and buds, also of an undetermined part, perhaps the whole of 
the parenchymatous tissue, which ramifies through the tubercle 
in every direction, surrounding and holding together the scler- 
enchyma patches and, as is shown in Plates II and III, pene- 
trating the as yet unchanged bast and wood of the oak root. 
To the host, on the contrary, besides its evident possessions, 
may be attributed the “ bark,” the sclerenchyma, and, possibly, 
a part of the ramifying parenchymatous tissue. 
The only argument against this is the fact easily seen in 
Plate IV, Figs. 1, 2, 3 and 4, that the patches of sclerenchyma 
are found at the base of flower shoots, in what is undoubtedly 
the tissue of the parasite. On the contrary, however, they 
are never found, except at the very base of the adult 
shoot. 
