192 BOTANICAL GAZETTE [mance 
ing the tissues below the flowers, thus causing the death of al 
the young pods above the point of attack. Before proceeding 
farther let us recall the structure of the bean flower, It wl 
be remembered that the pistil and the stamens are completely 
enclosed in the spirally coiled keel (fig. 7). No portion a 
them is exposed to view except the very base of the ovary, ant 
that only when the surrounding petals are forced apart. Under 
these conditions not only would close-fertilization seem tol 
assured, but it would appear certain that, however the milder | 
gained access to the host, it certainly could not be by infection 
of any part of the pistil before the fall of the flower. Yet, cot 
tinuous observation convinced me that the mildew failed 
appear to any serious degree before the flowers began to expat 
that fairly mature pods seldom showed areas of fresh infection : 
that the young pods often showed a copious growth of fruiting 
hyphe and spores indicative of infection before the fall of i 
blossom, and that the points of infection were always at the 
extreme base or tip of the young pods. These observations lef 
to the supposition that insects were mainly responsible for the 
dissemination of the mildew. 
Further investigation confirmed this view. I bavt ne 
attention to the enclosed and protected position occupied by : 
pistil; this obtains until the flower is visited by an insect of cor i 
siderable size, generally a honeybee. The projecting bee 
offer a convenient landing place, and, as the bee alights on a 
his weight deflects both wings and keel, the style ai J 
from the keel, the bee’s abdomen brushes over it, and in his ie J 
to reach the bottom of the flower the petals are forced apatt a 
base of the Ovary exposed and the bee's head comes pres : 
with it (figs. 2,3). Thus cross-fertilization is secured, butit bir 
has, by chance, touched a mildewed pod with either head of a 
men, fungous infection no less surely occurs. It will be of . 
the only portions of the pistil touched by the bee are gies — 
the ovary and the style. An examination of score - and a 
showed that in the majority of cases they were infect i e | 
these cases, without exception, the poin 
identical with the spots touched by the bees (f8- 
