12 Wilson — Obsa-vaiions 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, i 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, II and III can now be understood. Each of the three 

 tubercles in Plate I is the growth of a 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 to irritation 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 ho.st, 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, i, 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. 



