CHAP.V. LATHYRUS ODORATUS. 153 



PHASEOLUS VULGARIS. 



With respect to this species, I merely ascertained that the 

 flowers were highly fertile when insects were excluded, as indeed 

 must be the case, for the plants are often forced during the 

 winter when no insects are present. Some plants of two varieties 

 (viz., Canterbury and Fulmer's Forcing Bean) were covered with 

 a net, and they seemed to produce as many pods, containing as 

 many beans, as some uncovered plants growing alongside ; but 

 neither the pods nor the beans were actually counted. This 

 difference in self-fertility between P. vulgaris and midtiflorus is 

 remarkable, as these two species are so closely related that 

 Linnaeus thought that they formed one. When the varieties of P. 

 vulgaris grow near one another in the open ground, they some- 

 times cross largely, notwithstanding their capacity for self- 

 fertilisation. Mr. Coe has given me a remarkable instance of 

 this fact with respect to the negro and a white-seeded and 

 a brown-seeded variety, which were all grown together. The 

 diversity of character in the seedlings of the second generation 

 raised by me from his plants was wonderful. I could add other 

 analogous cases, and the fact is well known to gardeners.* 



LATHYRUS ODORATUS. 



Almost everyone who has studied the structure of papi- 

 lionaceous flowers has been convinced that they are specially 

 adapted for cross-fertilisation, although many of the species are 

 likewise capable of self-fertilisation. The case therefore of 

 Lathyrus odoratus or the sweet-pea is curious, for in this 

 country it seems invariably to fertilise itself. I conclude that 

 this is so, as five varieties, differing greatly in the colour of their 

 flowers but in no other respect, are commonly sold and come 

 true ; yet on inquiry from two great raisers of seed for sale, I 

 find that they take no precautions to insure purity the five 

 varieties being habitually grown close together.! I have myself 

 purposely made similar trials with the same result. Although 

 the varieties always come true, yet, as we shall presently see, one 



* I have given Mr. Coe's case ture,' 1872, p. 242, to the same 

 in the ' Gardeners' Chronicle,' effect. He once, however, saw 

 1858, p. 829. See also for another bees visiting the flowers, and sup- 

 case, ibid. p. 845. posed that on this occasion they 



t See Mr. W. Farley in 'Na- would have been intercrosses. 



