318 APPENDIX 



character for each, in so far that healthy plants, grown in the same 

 soil, are only subject to unimportant variations in this character. 



In experiments with this character, in order to be able to dis- 

 criminate with certainty, the long axis of 6 to 7 ft. was always 

 crossed with the short one of | ft. to 1| ft. 



Each two of the differentiating characters enumerated above 

 were united by cross-fertilisation. There were made for the 



1st trial 60 fertilisations on 15 plants. 



2nd " 58 " " 10 



3rd " 35 " " 10 



4th " 40 " " 10 



5th " 23 " " 5 



6th " 34 " " 10 



7th " 37 " " 10 



From a larger number of plants of the same variety only the most 

 vigorous were chosen for fertilisation. Weakly plants always afford 

 uncertain results, because even in the first generation of hybrids, 

 and still more so in the subsequent ones, many of the offspring 

 either entirely fail to flower or only form a few and inferior seeds. 



Furthermore, in aU the experiments reciprocal crossings were 

 effected in such a way that each of the two varieties which in one 

 set of fertilisation served as seed-bearer in the other set was used 

 as the pollen plant. 



The plants were grown in garden beds, a few also in pots, and 

 were maintained in their naturally upright position by means of 

 sticks, branches of trees, and strings stretched between. For each 

 experiment a number of pot plants were placed during the blooming 

 period in a greenhouse, to serve as control plants for the main 

 experiment in the open as regards possible disturbance by insects. 

 Among the insects ^ which visit Peas the beetle Bruchus pisi might 

 be detrimental to the experiments should it appear in numbers. 

 The female of this species is known to lay the eggs in the flower, 

 and in so doing opens the keel; upon the tarsi of one specimen, 

 which was caught in a flower, some pollen grains could clearly be 

 seen under a lens. Mention must also be made of a circumstance 



main axis of the plant. The unit of measurement, being indicated in the original 

 by a dash ('), I carelessly took to have been an inch, but the translation here given 

 is evidently correct.] 



^ [It is somewhat surprising that no mention is made of Thrips, which swarm in 

 Pea flowers. I had come to the conclusion that this is a real source of error and I see 

 Laxton held the same opinion. 1 



