72 
parasites, some of which had escaped by the three holes referred to 
above, while three mature insects were still to be seen within the 
A younger gall (Fig. 7) appears to be another example of the 
same kind. The body inside this gall (Fig. 8, 7.) is described by 
A transverse section of the leaf-rudiment from the apex of a 
normal mature gall is shown diagrammatically in Fig. 9. The 
parenchymatous cells of the mesophyll have thick walls and are 
practically devoid of contents ; the vascular bundles are collateral. 
The structural difference between the vascular bundles of the 
normal internode and those of the gall is shown in Figs. 13 and 14. 
A medium-sized bundle was chosen for illustration in both cases. 
The bundle from the gall (Fig. 14) shows considerable reduction in 
the size of the xylem-vessels and the elements of the phloem. This 
reduction in the size of the conducting elements of the vascular 
bundles is a marked feature in all the galls examined, and, in the 
case of the vessels, may be carried further than in Fig. 14, even in 
the largest bundles of a gall. This reduction may perhaps be con- 
nected with the rudimentary nature of the single leaf above the 
gall and the cessation of apical growth. 
Prof. Trail informs me that he has found a somewhat similar 
gall in Agropyrum repens,t but that certain characters of the gall in 
Ischaemum and of the insect producing it are exceptional. Thus 
possibly a perforation made by the ovipositor of the parasitic insect. 
other hand the egg of the parasite may be laid 1- 
hile it is still outside the eset Oe ee ee 
t Gf. Houard, Ann. Sci. Nat. Bot., sér. 8, p. 360, t. 20. 
} Houard, Les Zoocécidies des Plantes d’Europe (1908), vol. 1, p. 59. 
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