206 EEV. G. HENSLOW — FERTILISATION OF PLAXTS. 



thus superior to the (now crossed) self-fertilised. It did, as the 

 ratio, 100 to 82, indicates. This is nearer to unity than before, 

 hut it only shows that the self-feitilised plant was now benefited 

 by its being crossed, while the (twice) intercrossed retained some 

 benefit, but did not acquire any proportionally increased advan- 

 tage. The next was the sweet pea. In the first generations, 

 the intercrossed to the self -fertilised was 100 to 80, the next 

 year 100 to 88. Then he allowed both to be self-fertilised, and 

 the ratio was 100 to 90, or nearly 90. Then, he says, some were 

 cultivated in very unfavourable situations, and showed in an " un- 

 mistakable manner" the superior constitutional vigour in those 

 which had been intercrossed. He put some in a pot containing a 

 large Brugmmisia, and in poor soil, and the ratio was 100 to 88, 

 exactly that of the previous year. Again, when planted on poor soil 

 in the shrubbery, others reached 100 to 98, or practically showing 

 no difference between the intercrossed and self-fertilised, i.e. the 

 benefit of intercrossing was not transmitted. So from these two 

 cases I do not see that he is justified in attributing " evil eftects 

 to self-fertilisation." He established the fact that the benefits of 

 the cross may be handed down, but the "evil effects'' of self- 

 fertilisation are not proved. The self-fertilised were just as healthy. 

 He remarks that both produced a profusion of pods, and, in fact, 

 under the shrubbery they were practically equal in height. 



He adds a remarkable instance, where he says the effect of the 

 cross was carried on for a long period. A variety of the common 

 pea was raised by Mr. Knight by crossing distinct varieties, and it 

 retained its characters by self-fertilisation alone for npicards of 

 sixty years. If it was not superseded for sixty years as a market- 

 able product, the words " evil effects " are surely misleading. The 

 crossing has to thank the self-fertilising power of the pea for 

 keeping it up so long ! 



Now I will give you what seem to me the grounds for believing 

 in the benefits of self- fertilisation. You may think it strange after 

 what I have been saying, but in many cases I think it is true, and 

 Mr. Darwin himself admits it. Although he talks about the " evil 

 effects," yet he admits that in some cases self- fertilisation must be 

 beneficial. This was the case when the results were compai'od 

 witli those of crossing flowers on the same plant. The self-fertilised 

 plants of Iponuea were higher than the intercrossed. He says : 

 " This is a remarkable fact, which seems to show that self -fertili- 

 sation is more advantageous, unless the crossing brings some decided 

 and appreciable advantage." This is the clue to the whole thing. 

 Crossing is only a means to an end, and tliat end is the introduction 

 of new constitutional elements. Hence by means of intercrossing, 

 different plants, which are living under slightly different circum- 

 stances, have new elements of constitution introduced into each otlier; 

 and from this arises the benefit. Tlie mere act of crossing does no 

 good. It is similar or analogous to ourselves going to a difl'erent 

 part of the country for change of air. An invalid likes change and 

 new scenery, for they invigorate the constitution. So as long as a 



