Trelease.] 
438 
[March 15, 
manner. Taking advantage of the habit of many insects of visit- 
ing an inflorescence from below upward in both cases brings 
them to the older flowers first, and having fertilized these they 
later obtain pollen from the younger flowers to carry to other 
plants. 
In all of the examples taken there is much greater possibility 
of crossing than self-fertilization, even if the latter should prove 
not to be absolutely excluded in any, although it is apparently 
impossible in some. 
Though far less specialized than any of the others, Lemna is of 
more than usual interest. That so simple a plant should develop 
a flower, an organ which, simple as it is, possesses more complex 
parts than the entire plant beside, is remarkable. When, further, 
we recall that this flower is not cleistogene, but that its essential 
organs are exposed as in the generality of flowers, and moreover, 
that the structure and development of the parts favor cross-fer- 
tilization, we are led to believe there must be some special reason 
for effecting the latter. Far from depending upon the production 
of seed for ability to survive the winter, the plant produces in 
the autumn buds that are perfectly able to live until spring, and 
large numbers of them do so, and its great power to increase non- 
sexually has already been mentioned. The case offers unmistak- 
able presumptive evidence that continued propagation by non- 
sexual means or by close-fertilization is not best for the species, 
else there should not be so perfect an arrangement for crossing 
when either could have been secured with far less expenditure of 
material and energy. Although the contrivances in the other 
flowers I have described are more elaborate than in Lemna, the 
proportional specialization is greater in the latter. I need not 
add that the conclusion to which they all point is fully confirmed 
by the fact that in all phaenogams and many cryptogams means 
are provided for securing at least occasional crossing between dis- 
tinct stocks, as well as by the results of Mr. Darwin’s careful 
experiments in testing the effects of cross and self-fertilization. 
List of Works referred to in the Preceding Paper. 
Bentham, George. (1). Notes on the styles of Australian Proteaceae, 
(Journ. Linnean Soc., Bot., Apr. 6, 1871, xm, p. 58-64, pi. 1-2). 
