45 
THE FERTILISATION OF CERTAIN PLANTS 
(DIDYNAMIA). 
By WILLIAM OGLE, M.D. Oxon, F.R.C.P. 
Lecturer ox Physiology at St. George’s Hospital. 
[PLATE LVL] 
I N the July Number of this Review I described the fertilisa- 
tion of Salvia and of some other flowers.* I showed how in 
each case arrangements existed either entirely to prevent self- 
fecundation, or, at any rate, to render it of rare occurrence. I 
wish now to show that the same fact is observable in all didy- 
namia, and that the ordinary didynamous structure is indeed 
nothing more than a contrivance to facilitate intercrossing, and 
finds in its adaptation to this object its raison d'etre. 
I will begin with a flower abundant enough in our fields, the 
common red rattle ( Pedicularis sylv.). This has a labiate 
corolla, and, as is the general rule in this form of irregularity, 
the tube furnishes a sweet secretion to attract insects, while 
the lower lip forms for them a convenient landing-place. The 
upper lip or hood is remarkably flattened, as though the flower 
had been pressed in a book. The upper end of this hood is 
closed for some little distance in front completely, and the 
stigma projects from it just at the point where the complete 
closure ceases. Below this again, from the stigma down to the 
projecting point, marked a in the illustration (fig. 1), the hood 
is practically closed by the close approximation of the two sides, 
so that the stigma is effectually shut off both above and below 
from the interior of the hood. Below the projecting point the 
hood is open in front, but the fissure is very narrow because 
of the flattening already mentioned. The style rising from 
the two-celled ovary runs at the back of the corolla in the 
closest contact with it, following its contour exactly, and thus 
the curved outline of the closed part of the hood causes the 
style to bend round, and brings the stigma into the position it 
occupies. The stamens are four in number, two rather longer 
viz. Mallow, Lopezia, Larkspur. 
