210 EEY. G. HENSLOW FEKTILISATIOIT OF PLANTS. 



Animals and Plants under Domestication," he says that it is 

 necessary to put them under competition, otherwise little or no 

 difference may be seen in the results, showing, therefore, that, 

 apart from the competition, there is not so much benefit to the 

 intercrossed over the self- fertilised as might be expected. 12. 

 Naturalised abroad, self- fertilised plants often gain great vigour, 

 and are the fittest to survive in the struggle for life. I have 

 noted down all the Eritish plants from a number of diifcrent 

 lists of floras of foreign countries, to see what was the distribution 

 of our own wild flowers over the world; and what at once struck 

 me as peculiar was that they are, for the most part, the incon- 

 spicuous and self-fertilising flowers. Thus Cardamine hirsida is a 

 good example. You probably know C. prafensis, the "cuckoo 

 flower" of our meadows. While this is solely European, C. hirsuta 

 is found in many countries scattered over the world. Stellaria 

 media, the chickweed, is found in a great many places, but Stellaria 

 Solostea, the common stitchwort, which is large flowered and re- 

 quires insects, is nowhere to be found out of Europe. No other 

 species of Malva except M. rotundifoJia is widely dispersed : with 

 the sole exception of M. sylvestris, which is in Japan. There is no 

 reason why the conspicuous-flowered plants should not have become 

 dispersed as well as the others. Again, Solanum nigrum, the little 

 white flowering night-shade, is found dispersed, while Solanum 

 Dulcamara is nowhere seen but here. Polygonum ariculare, which 

 bears little inconspicuous green flowers, and is self-fertilising, is found 

 in Australia and elsewhere; but the large purple one, P. Pisforfa, is 

 only met with here. Moreover the former, a small weed in this 

 country, in New Zealand is completely ousting the Uiitivc flowers. 

 It is described as being four feet long, and with roots of seveial feet 

 in length. Now if such is the case, what ai-e we to infer? That 

 there is no appreciable reason why the conspicuous and insect- 

 requiring plants should not travel about as much as the incon- 

 spicuous ones ; but that if they did, and have disappeared, it is 

 because no insects visited them. Inasmuch as insects, as a rule, 

 keep to particular flowers, and the native insects in toreijin countries 

 would continue to visit their own flowers, and would not take the 

 trouble to go to the newly-imported individuals, I infer that, 

 whenever conspicuous forms reqniring insect agency have migrated, 

 they have generally perished— in other words, that the self-fertil- 

 ising are the fittest to survive in the struggle for lite. 



