120 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
experiments have demonstrated that this high degree of fertility is no 
longer rare, so that Darwin’s sentence, ‘‘ This high degree of fertility is, 
however, rare,” might now read, “ This high degree of sterility is, how- 
ever, rare.” 
Some statistics I prepared some time ago,* and now made up to date, serve 
as an illustration of this from the Orchidew. During the past seven years 
Mr. Reginald Young, of Liverpool, the well-known orchidist, has been cross- 
ing inter se some 30 distinct species and 58 distinct hybrids in the genus 
Paphiopedilum (Pfitz), and has kindly placed his stud book at my disposal, 
in which are precisely and carefully recorded no less than 849 crosses. 
Of these, taken together, 80°2 % have proved fertile, 7.e. produced good 
seeds. Of 263 crosses between distinct species 95:0 % were fertile. This 
seems to show that in this genus crosses between distinct species are 
almost, if not quite, as fertile as crosses between varieties of the same 
species (taking the latter at complete fertility, 2.e. 100% ); while in 
crosses in which a hybrid was concerned in the parentage, out of 586, 
only 73°5 % proved fertile, showing that crosses with hybrids, though 
fertile to a high degree, are yet rather less fertile than crosses between 
species. 
A further analysis of the figures shows that while hybrids crossed 
with the pollen of pure species give 91°8 % fertile, yet pure species 
crossed with the pollen of hybrids give but 60 % tertile. This seems to 
point to the conclusion that the slight decline in the fertility of 
hybrids is due in a large measure to the loss of power in the pollen 
of hybrids. 
This decline of power in the male element of hybrids is very curious, 
but has been observed before in other plants by Darwin, Dr. Focke, Dr. 
Maxwell Masters, and Prof. Macfarlane, and also by Prof. Ewart in his 
Zebra hybrids. Practical breeders will therefore be wise, in crossing 
hybrids with species, to always use the pollen of species in preference to 
that of hybrids. 
It is quite possible that domestication or cultivation may in time eradi- 
cate this decline in the fertility of hybrids, for I observe that in my hybrid 
Berbevis x stenophylla, the first hybrids between the two wild species 
flower more profusely, but bear fewer berries than the parent species ; 
while the hybrids of the second generation are much more profuse in their 
berry-bearing, being apparently more fruitful even than the wild species. 
It very often happens that the pollen of very young hybrids is not so effec- 
tive as that of those of more mature growth. Mr. Reginald Young believes 
this to be so with his Paphiopedilums ; and Dr. Focke records a case of a 
hybrid Sinningia in which the pollen of the second year of flowering 
was better than that of the first. The decline of fertility is by no means 
confined to hybrids alone ; for instance, certain races of Primula sinensis 
raised by Messrs. Sutton, of Reading, have proved difficult to perpetuate 
owing to their diminished fertility, and these are cross-breds, not hybrids, 
being raised within the limits of one species. 
In the face of these facts, therefore, we must conclude that fertility 
depends more upon the conditions of life than upon hybridism, and there 
is no reason why hybrids should not in time become as fully fertile as 
cross-breds usually are. 
* See Jowr. Roy. Hort. Soc. xxi. (April, 1898], p. 485 
