Annual Report for 1908 of the Zoologist. 323 
it, as it grows, the keel, now detached from the flower base, 
so that a young pod, say an inch long, is still surrounded by 
the calyx and the remains of the stamen sheath at its fixed 
end, while its free end is capped by the detached keel. If 
diseased, the little yellow larvae of the thrips will be found 
mostly concealed under the shelter thus afforded at either end 
of the pod, and from these hiding places the injury begins, 
and gradually advances over the whole pod. Discoloured 
patches appear, interrupting the even greenness which charac- 
terises the clean and healthy pod. The patches, which are 
generally whitish, look very much as though the surface had 
been nibbled away. This is not the case, however, for if the 
outer skin of the pod be peeled off, it is found to be entire, 
even over the injured portions. The insects do not bite, 
though the contrary is sometimes stated. They pierce very 
minute holes in the skin and suck the sap, and the discoloura- 
tion is due to the injury thus inflicted on the subjacent tissues. 
The discolouration is quickly followed by distortion, the pod 
Fia. 2.— A young diseased pod, enlarged. 
losing its straightness and curling in a very unsightly manner. 
Fortunately, as the disease is on the outside of the pod, the 
seeds are the last to suffer, and quite tolerable peas can often 
be taken from very disagreeable-looking pods. For ordinary 
purposes, however, the appearance of the pods is almost as 
important as that of the peas themselves. Moreover, a stage 
is often reached where a fungoid disease aggravates the injury 
done by the thrips, and the whole pod becomes blackened and 
decayed. When this is the case with the older pods, it will 
be found that many of these at an earlier stage are killed 
outright and come to nothing, so that the whole yield may be 
very greatly reduced. 
The insects concerned . — The minute insects known as 
thrips constitute an order by themselves, the Thysanoptera. 
Haliday investigated the English species about seventy years 
ago, and no one in this country seems to have paid much 
