IN THE VEGETABLE KINGDOM 53 



be led to bear a still heavier crop next year ; whereas 

 it is apt to be wholly or partially barren next year 

 has to recover a state of tolerably high nutrition before 

 its sexual genesis again becomes large." x 



Spencer does not make it clear why, on his theory, 

 it should be impolitic to dung the roots of a fruit-tree 

 while the growth of sexless axes is still luxuriant. On 

 the theory sketched out here, it is because the growth 

 of sexless axes is a sign that the degree of nutrition has 

 passed the point which is adapted to produce the maxi- 

 mum degree of sexual fertility. As Spencer points out, 

 the change from the production of seed-bearing fruit to 

 the production of sexless axes is a change from sexual 

 to asexual genesis. This latter can be dealt with later, 

 but it may be noted that Spencer's theory makes no 

 provision for the fact, clearly shown in the above extract, 

 that the conditions most favourable to asexual genesis 

 are inimical to the sexual process. 



In the large body of evidence brought together by 

 Darwin bearing on this question, not a single fact is 

 mentioned inconsistent with the theory. A number of 

 facts are given which at first sight appear capricious 

 or of ambiguous interpretation. Thus a plant is men- 

 tioned which " is a native of the moderately warm banks 

 of the Plata, seeds freely in the hot, dry country near 

 Lima, and in Yorkshire resists the severest frosts, and 

 I have seen seed gathered from pods which had been 

 covered with snow during three weeks." 2 But this 

 merely points to a wide range of adaptation due to some 

 peculiarity of constitutional organisation, such as that 

 which enables some men to endure vast changes of tem- 

 perature and suffer little inconvenience, while others are 



1 Principles of Biology, vol. ii, chap. ix. 



* Variation of Animals and Plants under Domestication, chap, xviii. 



