160 MR. R. A. ROLFE ON 
tained swollen seed-pods, but their contents have invariably 
turned out to be nothing but chaff; at least, he has never suc- 
ceeded in inducing any seed to germinate. And there are many 
other instances within the limits of the Order where species of 
the same genus, and in some cases closely allied species, have 
hitherto successfully resisted all the arts of the hybridizer to effect 
a cross between them. 
So that, without insisting too strongly on the value of every 
item of negative evidence adduced, we are still justified in as- 
suming that while in some instances hybridization may be 
effected between species belonging to diverse genera, yet in other 
cases it may not be effected even between species belonging to 
the same genus. 
The question here naturally arises, Are these genera which 
may be hybridized together really distinct ? A negative answer 
is sometimes given to this query, though an affirmative one is 
more in harmony with the gradually accumulating evidence on 
the subject. To deny the distinctness of genera between which 
hybridization can be (artificially) effected differs only in degree 
from what was once maintained with respect to species, namely 
that so-called species which would hybridize together were not 
really distinct, but only forms of the same species. But this 
theory is now completely exploded; and it seems to me that, 
with respect to genera, the idea will also have to be given up, a8 
the analogy between the two cases is so very close. This 
analogy may be readily expressed in diagrammatic form as 
follows :— 
TABLE I., showing how Cypripedium barbatum has been connected 
with other species by artificial hybridization. 
T 16 
= 6 19 
Soy ù 
