With cart-mares, which sometimes will not breed with stallions of pure blood, but subsequently have bred with cart-stallions, Mr. Spooner is inclined to attribute the failure to the lesser sexual power of the racehorse. But I have heard from the greatest breeder of racehorses at the present day, through Mr. Waring, that "it frequently occurs with a mare to be put several times during one or two seasons to a particular stallion of acknowledged power, and yet prove barren; the mare afterwards breeding at once with some other horse." These facts are worth recording, as they show, like so many previous facts, on what slight constitutional differences the fertility of an animal often depends.]
STERILITY OF PLANTS FROM CHANGED CONDITIONS OF LIFE, AND FROM OTHER CAUSES.
In the vegetable kingdom cases of sterility frequently occur, analogous with those previously given in the animal kingdom. But the subject is obscured by several circumstances, presently to be discussed, namely, the contabescence of the anthers, as Gartner has named a certain affection--monstrosities-- doubleness of the flower--much-enlarged fruit--and long-continued or excessive propagation by buds.
[It is notorious that many plants in our gardens and hot-houses, though preserved in the most perfect health, rarely or never produce seed. I do not allude to plants which run to leaves, from being kept too damp, or too warm, or too much manured; for these do not flower, and the case may be wholly different. Nor do I allude to fruit not ripening from want of heat or rotting from too much moisture. But many exotic plants, with their ovules and pollen appearing perfectly sound, will not set any seed. The sterility in many cases, as I know from my own observation, is simply due to the absence of the proper insects for carrying the pollen to the stigma. But after excluding the several cases just specified, there are many plants in which the reproductive system has been seriously affected by the altered conditions of life to which they have been subjected.
It would be tedious to enter on many details. Linnaeus long ago observed (18/78. 'Swedish Acts' volume 1 1739 page 3. Pallas makes the same remark in his 'Travels' English translation volume 1 page 292.) that Alpine plants, although naturally loaded with seed, produce either few or none when cultivated in gardens. But exceptions often occur: the Draba sylvestris, one of our most thoroughly Alpine plants, multiplies itself by seed in Mr. H.C. Watson's garden, near London; and Kerner, who has particularly attended to the cultivation of Alpine plants, found that various kinds, when cultivated, spontaneously sowed themselves. (18/79. A. Kerner 'Die Cultur der Alpenpflanzen' 1864 s. 139; Watson 'Cybele Britannica' volume 1 page 131; Mr. D. Cameron also has written on the culture of Alpine plants in 'Gard. Chronicle' 1848 pages 253, 268, and mentions a few which seed.) Many plants which naturally grow in peat-earth are entirely sterile in our gardens. I have noticed the same fact with several liliaceous plants, which nevertheless grew vigorously.
Too much manure renders some kinds utterly sterile, as I have myself observed. The tendency to sterility from this cause runs in families; thus, according to Gartner (18/80. 'Beitrage zur Kenntniss der Befruchtung' 1844 s. 333.), it is hardly possible to give too much manure to most Gramineae, Cruciferae, and Leguminosae, whilst succulent and bulbous-rooted plants are easily affected. Extreme poverty of soil is less apt to induce sterility; but dwarfed plants of Trifolium minus and repens, growing on a lawn often mown and never manured, were found by me not to produce any seed. The temperature of the soil, and the season at which plants are watered, often have a marked effect on their fertility, as was observed by Kolreuter in the case of Mirabilis. (18/81. 'Nova Acta Petrop.' 1793 page 391.) Mr. Scott, in the Botanic Gardens of Edinburgh, observed that Oncidium divaricatum would not set seed when grown in a basket in which it throve, but was capable of fertilisation in a pot where it was a little damper.