180 MR. ©. DARWIN ON THE SEXUAL RELATIONS OF 
the more fertile {unions ; but it rendered the less fertile unions 
even more sterile than they otherwise would have been. I have 
seen striking instances of this same fact in making homomorphie 
and heteromorphic unions in Primula*; and it is well known 
that the conditions of life must be highly favourable to give any 
chance of producing hybrids from species which cross with diffi- 
culty. 
Table I.— Lone-stytEp Form. 
| | L II. 
| 18 flowers fertilized bythelonger| 13 flowers fertilized by the longer 
| stamens of the mid-styled. These | stamens of the short-styled. These 
| stamens equal in length the pistil of | stamens equal in length the pistil of 
| the long-styled. the long-styled. 
| Product of good seed in each capsule. | Product of good seed in each capsule. 
| 36 53 159 104 
| 81 0 43 119 
| 0 0 96 poor seed. 96 
| 0 0 103 99 
| 0 0 0 131 
| — 0 0 116 
| 45 — 
| 41 114 
| 
38 per cent. of these flowers yield- | 84 per cent. of these flowers yield- 
| ed capsules. Each capsule contain- | ed capsules. Each capsule con- 
| ed, on an average, 51:2 seed. tained, on an average, 107:3 seed. 
* In the spring of 1862 I crossed forty Cowslip flowers (P. veris) hetero- 
morphically and homomorphically. The plants were accidentally exposed in 
the greenhouse to too hot a sun, and a number of umbels perished. Some, 
however, remained in moderately good health, and on these there were twelve 
flowers which had been fertilized heteromorphically and eleven which had been 
fertilized homomorphically. The twelve heteromorphie unions yielded seven fine 
capsules, containing on an average 57-3 good seed. Now mark the difference: 
the eleven homomorphic unions yielded only two capsules, of which one con- 
tained 39 seeds, but so poor, that I do not suppose one would have germinated, 
and the other only 17 fairly good seed. It would be superfluous to give any 
more details on this experiment, or on some which I made at the same time on 
P. Sinensis, after the appearance of Mr. John Scott’s admirable paper on the 
various dimorphic species of Primula, in which he confirms my former results, 
and adds many original and valuable observations. Dr. Hildebrand has also 
(Botanische Zeitung, 1864, Jan.1, 8. 3) confirmed my general results with respect 
to P. Sinensis, and has corrected an error into which in some unaccountable 
manner I fell, namely, that the pollen-grains from the long- and short-styled 
forms were of the same size. Dr. Hildebrand has added a series of new and 
important experiments, for he fertilized homomorphically a number of flowers 
with pollen from the same form, and likewise from the same individual flower. 
These latter he found were thus rendered rather more sterile. This experiment, 
I believe, has never been systematically tried before. 
