ON HYBRIDIZATION AMONG- PLANTS. 
BY REV. G. HENSLOW, M.A., F.L.S. 
H YBRIDISM in plants has long engaged the attention of 
many accurate observers; and the importance of it, as 
assisting us to arrive at more definite knowledge of the 
phenomena of plant life, can scarcely be overrated. Investi- 
gations in hybridism are valuable to the systematic and physio- 
logical botanist, to the horticulturist, and those who are 
interested in attempting the so-called “ acclimatization ” of 
plants. To the systematic botanist the study is useful as 
showing him, when positive results are obtained, that either 
the parent forms of any hybrid must be grouped under the 
same (natural) genus, or that they may at least be sus- 
pected to have had a common origin. Thus the late 
Dean Herbert crossed Amaryllis and Crinum. Hence these, 
as well also as the three genera. Rhododendron, Rhodora, 
and Azalea, which have been found capable of blending, must 
(he says) form a single genus respectively. But with negative 
results the systematist gains but little ; for he can by no means 
draw an opposite conclusion, and say that forms must be of 
separate genera because his attempts have failed to secure 
a hybrid. For many species, apparently distantly allied, 
fertilize one another with avidity ; whereas others, assumed to 
be most intimately connected, absolutely refuse all attempts to 
make them blend. These negative results would seem therefore 
to impede rather than aid the systematic botanist. Yet the fact 
of their furnishing no fertile offspring does not necessarily 
warrant us in saying they never can or would propagate any 
hybrid forms. Indeed, the causes of sterility are so numerous, 
the process of fecundation so complicated, and the difficulties, 
constitutional, climatal, &c., are so great, in certain cases 
when cross-fertilization is attempted, that it is not to be 
wondered at if fertile offspring are not produced on every 
occasion. To show how complicated is the process, we may 
mention that repeated applications of pollen are believed 
(Gaertner) to be sometimes requisite to overcome the natural 
