EXPERIMENTS IN HYBRIDISATION, &c. 119 
(8) Hybrids between Aquilegia californica and A. chrysantha, and A. 
cerulea and A. chrysantha crossed water sc, by Mr. James Douglas, 
yielded an extraordinary variety of forms, being several generations of 
three species. 
(9) The new race of Streptocarpus, raised at Kew, are from the inter- 
crossing of hybrids between the three species, 8. Dunni, S. Rexi, and S. 
parviflorus. * 
(10) Our garden Roses are the product of the hybridisation through 
many generations of at least three species, viz. R. gallica, R. indica, 
and R. multiflora; while Lord Penzance has raised hybrids between R. 
lutea and R. rubiginosa which are fertile, both self-crossed, and also with 
the race of Hybrid Perpetuals, raised originally from R. gallica and R. 
indica. Here we have hybrids of four distinct species. 
(11) The Amaryllis or Hippeastrum of gardens have been derived from 
hybrids of many generations, of several species. 
(12) Gladiolus x Nanceianus is a hybrid of the third generation, 
uniting the four species G. psittacinus, G. oppositiflorus, G. Saundersi, 
and G. purpurato-auratus. 
(18) The Orchid-flowering Cannas ‘ Italia,’ ‘Austria,’ ‘ Burbank,’ 
&e., are the third generation of four species, namely C. iridiflora, C. War- 
scewiczii, C. glauca, and C. flaccida. 
(14) In Paphiopedilum (Pfitz) (known in gardens as Cypripedium), 
twenty-eight hybrids have been recorded, each combining in its pedigree 
four distinct species.* 
(15) Rhododendron ‘Kos,’ raised by Mr. Heale, for Messrs. Veitch, 
of Chelsea, is a hybrid of the fourth generation, of four distinct species, 
viz. R. javanicum, R. jasminiflorum, R. Lobbii, and R. Malayanum ; 
while R. ‘Numa,’ raised by the same firm, is a hybrid of the fifth 
generation, and contains the five following species :—R. javanicum, R. 
jasminiflorum, R. Brookianum racile, R. indicum (Azalea indica Stella), 
and R. multicolor Curtisu. (Figs. 40 and 41.) 
But there is another phase of the question, which is of some import- 
ance, and that is the diminished fertility of some hybrids as compared 
with the fertility of natural species, and it is here probably that the 
popular idea of the infertility of hybrids first arose. Darwin, who made 
a most elaborate survey of the whole question, used the word ‘“ sterility,”’ 
not in the general sense of barrenness, 7.¢. absolute infertility, but simply 
in the sense of diminished fertility, standing as it were midway between 
complete fertility and absolute infertility ; so that when he wrote of the 
“sterility of hybrids,” he simply meant their lessened fertility, and not 
their infertility as most people seemed to imagine. Darwin, after careful 
research and many experiments, came to the following conclusion upon 
the whole matter, that “the sterility of distinct species when first 
united, and that of their hybrid offspring, graduates by an almost infinite 
number of steps from zero (when the ovule is never impregnated and a 
seed-capsule is never formed) up to complete fertility.”t This general 
statement is as true to-day as it was then. Darwin then goes on to say 
that “... this high degree of fertility is, however, rare.’’ Recent 
* See Orch. Rev. iv. p. 361. 
+ Animals and Plants, 2nd ed. ii. p. 163. 
