[50]

23d

L. Peregrinus Stipule — stem tied

(Used)

plant in same position as yesterday day moderately cloudy

8º a.m

8º 15' up

8º 50' down

9º 20'

10º

10º 30' — turned to light

10º 53'

11º 29' rising

12º

12.25 almost horizontal to light

12.45'

1º 23'

2.15' up — again

3º

3º 50' almost staying up

4º 35'

5º suppose not of glass

(17)

[50v]

[page not in Darwin's hand]

certainly not specially acquired quality; but is incidental, like the incapacity of certain trees to be grafted together, on other acquired differences. The nature of these differences is unknown, but they relate more especially to the reproductive system, & not to ordinary structure or to ordinary differences in constitution. The most probable conjecture is that they result from one r both of the crossed species having been long habituated to certain fixed conditions; for we know that changed conditions have a special influence on the reproductive system, & we have good reason to believe (as before remarked) that the fluctuating conditions of domestication tend to eliminate that sterility which is so general with species [illeg] under in the state of nature. it has been elsewhere shown by me (ibid. Vol. 2. p. 185, & Origin of Species 5th edit. p. 317) that the sterility of crossed species has not been acquired through natural selection: we can see that when two forms are already very sterile together, it is scarcely possible that their sterility should be

(over)

[Descent 1: 222-3, n13: "'The Variation of Animals and Plants under Domestication,' vol. ii. p. 109. I may here remind the reader that the sterility of species when crossed is not a specially-acquired quality; but, like the incapacity of certain trees to be grafted together, is incidental on other acquired differences. The nature of these differences is unknown, but they relate more especially to the reproductive system, and much less to external structure or to ordinary differences in constitution. One important element in the sterility of crossed species apparently lies in one or both having been long habituated to fixed conditions; for we know that changed conditions have a special influence on the reproductive system, and we have good reason to believe (as before remarked) that the fluctuating conditions of domestication tend to eliminate that sterility which is so general with species in a natural state when crossed. It has elsewhere been shewn by me (ibid. vol. ii. p. 185, and 'Origin of Species,' 5th edit. p. 317) that the sterility of crossed species has not been acquired through natural selection: we can see that when two forms have already been rendered very sterile, it is scarcely possible that their sterility should be augmented by the preservation or survival of the more and more sterile individuals; for as the sterility increases fewer and fewer offspring will be produced from which to breed, and last only single individuals will be produced, at the rarest intervals. But there is even a higher grade of sterility than this."]