Chap. XVIII. CHANGED CONDITIONS. 163 



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 — double- 

 ness 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 produce the reproductive 

 individual or flower, and the case may he 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 re- 

 productive 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. Linngeus long ago 

 observed 74 that Alpine plants, although naturally loaded with seed, pro- 

 duce 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. 75 Many plants which naturally grow in peat-earth are entirely 

 sterile m 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/ 6 it is hardly possible to give too much manure 

 to most Grammese, CruciferaB, and Leguminosse, whilst succulent and 

 bulbous-rooted plants are easily affected. Extreme poverty of soil is less 



7< , Swedish Acts,' vol. i., 1739, p. 3. D. Cameron, also, has written on the 



Pallas makes the same remark in his culture of Alpine plants in 'Gar J 



Travels (Eng. translat), vol. i. p. 292. Chronicle,' 1848, pp. 253 268 and 



^ A. Kerner, « Die Cultur der Alp- mentions a few which seed ' 

 enpflanzen,; 1864 s 139; Watson's 76<Beitrage zur Kenntniss der 



Cybele Bntanmca, vol. l. p. 131 ; Mr. Befruchtung,' 1844, s. 333. 



M 2 



