APPENDIX 319 



which possibly might lead to the introduction of foreign pollen. 

 It occurs, for instance, in some rare cases that certain parts of an 

 otherwise quite normally developed flower wither, resulting in a 

 partial exposure of the fertilising organs. A defective development 

 of the keel has also been observed, owing to which the stigma and 

 anthers remained partially uncovered.^ It also sometimes hap- 

 pens that the pollen does not reach full perfection. In this event 

 there occurs a gradual lengthening of the pistil during the bloom- 

 ing period, until the stigmatic tip protrudes at the point of the keel. 

 This remarkable appearance has also been observed in hybrids of 

 Phaseolus and Lathyrus. 



The risk of false impregnation by foreign pollen is, however, a 

 very slight one with Pisum, and is quite incapable of disturbing the 

 general result. Among more than 10,000 plants which were care- 

 fully examined there were only a very few cases where an indubi- 

 table false impregnation had occurred. Since in the greenhouse 

 such a case was never remarked, it may well be supposed that 

 Brnchus pisi, and possibly also the described abnormalities in the 

 floral structure, were to blame. 



[Fi] The Forms of the Hybrids ^ 



Experiments which in previous years were made with ornamental 

 plants have already afforded evidence that the hybrids, as a rule, 

 are not exactly intermediate between the parental species. With 

 some of the more striking characters, those, for instance, which 

 relate to the form and size of the leaves, the pubescence of the 

 several parts, &c., the intermediate, indeed, is nearly always to be 

 seen; in other cases, however, one of the two parental characters 

 is so preponderant that it is difficult, or quite impossible, to detect 

 the other in the hybrid. 



This is precisely the case with the Pea hybrids. In the case of 

 each of the seven crosses the hybrid-character resembles ^ that of 

 one of the parental forms so closely that the other either escapes 



^ [This also happens in Sweet Peas.] 



^ [Mendel throughout speaks of his cross-bred Peas as " hybrids," a term which 

 many restrict to the oflFspring of two distinct species. He, as he explains, held this 

 to be only a question of degree.] 



' [Note that Mendel, with true penetration, avoids speaking of the hybrid- 

 character as " transmitted " by either parent, thus escaping the error pervading the 

 older views of heredity.) 



