506 
PACIFIC SCIENCE, Vol. XIX, October 1965 
Fig. 5. Defoliation of branch of Hoheria sexsty- 
losa Col. caused by galls. 
is some analogy with the invaginating growth 
movements of the developing animal gastrula 
which is concerned with seclusion and shelter 
of germinal tissues from the external environ- 
ment — in the same sense that the embryonic 
mites are protected from the rigours of the out- 
side world by the invaginated gall-cavity in 
which they grow. 
SUMMARY 
The solid perennial galls frequently found 
on cultivated trees of Hoheria sexstylosa Col. 
are caused by the gall mite Eriophyes hoheriae 
Lamb. Most galls arise from transformed flower 
buds in late summer, but some galls occur on 
leaves. Persistence of galls often results in leaf- 
less unsightly branches. 
Within the galls, colonies of mites and their 
eggs are enclosed in sac-like cavities with puck- 
ered mouths, which are ringed by pointed epi- 
dermal hairs. 
Each cavity is lined by a zone of meristematic 
cells which act as a growth region analogous to 
the shoot growing point of angiosperms. 
Vascular traces arise in the vicinity of each 
"pouch metis tern" and differentiate back towards 
the older vascular strands. In this way is formed 
an efficient conducting system which radiates 
from the gall stalk and allows growth of the 
galls and mites to continue for some years, to 
the detriment of the rest of the tree. 
The cellular make-up of the galls is not es- 
sentially different from that of the normal 
shoot of Hoheria sexstylosa , but the pattern of 
growth is unique and advantageous to the mites 
and their embryonic young. 
ACKNOWLEDGMENT 
I am indebted to the former University of 
New Zealand (now the University Grants Com- 
mittee) for a research grant in aid of this work. 
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Boysen-Jensen, P. 1948. Formation of galls 
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