'm* 





164 



STERILITY FROM CHANGED CONDITIONS. Chap. XVIII 



ifol 



growing on a lawn often mown and never manured, did not 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 



t T7-»i i • j 1 _ _f« T\/T_* 1. 'I* 77 1%/r r* ii • n -r^ . 



Mirabilis 



of Edinburgh observed that Oncidium divaricatum would not set seed 

 when grown in a basket in which it throve, but was capable of fertili- 



sation in a pot where it was a little damper. 



fvlgid 



many years after its introduction, seeded freely; it then became sterile- 

 now it is fertile ;8 if kept in a dry stove during the winter. Other varie- 

 ties of pelargonium are sterile and others fertile without our being able 

 to assign any cause. Very slight changes in the position of a plant, 

 whether planted on a bank or at its base, sometimes make all the dif- 

 ference in its producing seed. Temperature apparently has a much more 

 powerful influence on the fertility of plants than on that of animals. 

 Nevertheless it is wonderful what changes some few plants will withstand 

 with undiminished fertility : thus the Zephyr antlies Candida, a native of the 

 moderately warm banks of the Plata, sows itself in the hot dry country 

 near Lima, and in Yorkshire resists the severest frosts, and I have seen 

 seeds gathered from pods which had been covered with snow during three 

 weeks. 79 Berberis Wallichii, from the hot Khasia range in India, is un- 

 injured by our sharpest frosts, and ripens its fruit under our cool summers. 

 Nevertheless I presume we must attribute to change of climate the 

 sterility of many foreign plants; thus the Persian and Chinese lilacs 



(Syringa Persica and Chinensis), thou 



duce a seed; the common lilac (S. vulgaris) seeds with us moderately well, 

 but in parts of Germany the capsules never contain seed. 80 



Some of the cases, given in the last chapter, of self-impotent plants, 

 which are fertile both on the male and female side when united with 

 distinct individuals or species, might have been here introduced ; for as 

 this peculiar form of sterility generally occurs with exotic plants or with 

 endemic plants cultivated in pots, and as it disappeared in the Passiflora 

 alata when grafted, we may conclude that in these cases it is the result of 

 the treatment to which the plants or their parents have been exposed. 



The liability of plants to be affected in their fertility by slightly changed 

 conditions is the more remarkable, as the pollen when once in process of 

 formation is not easily injured ; a plant may be transplanted, or a branch 

 with flower-buds be cut off and placed in water, and the pollen will be 

 matured. Pollen, also, when once mature, may be kept for weeks or even 

 months. 81 The female organs are more sensitive, for Gartner 82 found that 

 dicotyledonous plants, when carefully removed so that they did not m 

 the least flag, could seldom be fertilised ; this occurred even with potted 



77 « Nova Acta Petrop.,' 1793, p. 391. 



78 < Cottage Gardener/ 1856, pp. 44, 



109. 



79 Dr. Herbert, ' Amaryllidacese,' p. 



176. 



80 



Gartner, * Beitrage zur Kenntniss/ 



&c, s. 560, 564. 



81 < Gardener's Chronicle,' 1844, p. 



215 ; 1850, p. 470. 

 82 'Beitrage zur 

 252, o33. 



Kenntniss,' &c, s. 



