108 GOOD FROM CROSSING. Chap. XVII. 



Herbert also says/"^ " I am inclined to think that I have derived 

 "advantage from impregnating the flower from which I wished 

 " to obtain seed with pollen from another individual of the same 

 " variety, or at least from another flower, rather than with its 

 " own." Again, Professor Lecoq ascertained that crossed offsj)ring 

 are more vigorous and robust than their parents.^^ 



General statements of this kind, however, can seldom be fully 

 trusted : I therefore began a long series of experiments, continued 

 for about ten years, which will I think conclusively show the 

 good effects of crossing two distinct plants of the same variety, 

 and the evil effects of long-continued self- fertilisation. A clear 

 light will thus be thrown on such questions, as why flowers are 

 almost invariably constructed so as to permit, or favour, or necessi- 

 tate the union of two individuals. We shall clearly understand 

 why monoecious and dioecious, — why dichogamous, dimorphic and 

 trimorphic plants exist, and many other such cases. I intend soon 

 to publish an account of these experiments, and I can here give only 

 a few cases in illustration. The plan which I followed was to grow 

 plants in the same pot, or in pots of the same size, or close together in 

 the open ground ; carefully to exclude insects ; and then to fertilise 

 some of the flowers with pollen from the same flower, and others 

 on the same plant with pollen from a distinct but adjoining plant. 

 Ill many of these experiments, the crossed plants yielded much 

 more seed than the self-fertilised plants ; and I have never seen 

 the reversed case. The self-fertilised and crossed seeds thus 

 obtained were allowed to germinate in the same glass vessel on 

 damp sand ; and as the seeds germinated, they were planted 

 in pairs on opposite sides of the same pot, with a superficial 

 partition between them, and were placed so as to be equally ex- 

 posed to the light. In other cases the self-fertilised and crossed 

 seeds were simply sown on opposite sides of the same small pot. 

 I have, in short, followed different plans, but in every case have 

 taken all the precautions which I could think of, so that the two 

 lots should be equally favoured. The growth of the plants raised 

 from the crossed and self-fertilised seed, were carefully observed from 

 their germination to maturity, in species belonging to fifty-two 

 genera; and the difference in their growth, and in withstanding 

 unfavourable conditions, was in most cases manifest and strongly 

 marked. It is of importance that the two lots of seed should be 

 sown or planted on opposite sides of the same pot, so that the seed- 

 lings may struggle against each other; for if sown separately in 

 ample and good soil, there is often but little difference in their growth. 



I will briefly describe two of the first cases observed by me. 

 Six crossed and six self-fertilised seeds of Jpomoea purpurea, from 

 plants treated in the manner above described, were planted as soon 

 as they had germinated, in pairs on opposite sides of two pots, 

 and rods of equal thickness were given them to twine up. Five 



' Amaryllidaceae,' p. 371. " 'De la Fecondatioo,' 2n'l edit., 1862, p. 79. 



