SUPPLEMENT 117 



intermediate between the two parents arise. Further, the individual members 

 of the hybrid race may show differences, some being more like the father, 

 some more like the mother, and finally parts of the single individual may show 

 differences among themselves, one part displaying paternal, the other maternal 

 characteristics. 



1. 51 P- 374, 1. 51, for Although the hybrid . . . white-flowered, read As 

 an instance of an intermediate hybrid we may quote what KOLREUTER wrote 

 as to the first ' botanical cross ', the hybrid Nicotiana rustica $> x N. panicu- 

 lata a* : ' I was gratified to find that the hybrid took a median place between 

 the two parents not only in the arrangement of the branches, and in the position 

 and colour of the flowers, but also in all the parts of the flower (the stamens 

 alone excepted), which exhibited an almost geometrical mean.' 



In studying the hybrids of the second generation, i.e. the plants arising 

 from self-fertilized hybrids of the first generation, we will select a pea hybrid 

 which has sprung from a white- crossed by a red-flowering form, and which, 

 as we saw, has red flowers. 



375, 11. 36-45, for MENDEL'S law . . . fertilization, read This so-called ' law 

 of segregation ' has a wide but not a universal application ; perhaps it is 

 truer of hybrids between closely-related varieties than of specific hybrids. 

 The segregation may appear in one character though it is lost in another, and 

 segregation may result in the characters which are subject to the law of 

 prevalency as well as in others which lead to an intermediate hybrid. 



In the last case the results of segregation are exceedingly instructive. 

 If a white-flowered plant of MiraUlis Jalapa be crossed with a red-flowered, 

 the hybrid has light rose-coloured flowers. In the second generation, however, 

 25 per cent, of the flowers are pure white, 25 per cent, rose, and 50 per cent, 

 light-rose. It is possible here also to distinguish the individuals which are 

 still hybrids, and which segregate further from those which revert to the 

 pure type. 



Besides the laws of prevalency and of segregation, MENDEL has advanced 

 a third and very important observation, which may be termed the law of 

 ' independence of characters '. This shows itself when the two crossed races 

 differ in more than one point. If the white-flowered peas have yellow coty- 

 ledons, and the red-flowered, green, the colour of the cotyledons of the hybrids 

 is yellow. Hence one sees that it is not simply a case of one type maintaining 

 a struggle for supremacy against another, but that individual characters 

 struggle among themselves, sometimes one and sometimes another being 

 successful. Hence also each character of the plant must have a distinct initial 

 in the germ, and we cannot rest satisfied with the assumption of ' a specific 

 structure ' in a race from which its various characteristics arise. 



From the law of independence of characters it may be further assumed 

 that on the commencement of segregation in the second generation, forms 

 must also arise which possess a combination of characters not possessed by 

 the original races, e.g. white-flowered peas with green and red-flowered with 

 yellow cotyledons. If the parents differ in more than two characters the com- 

 plexity rapidly increases. CORRENS says that, with ten different characters, 

 the second generation must present thousands of externally different, and 

 almost 60,000 internally different, individuals. 



Such new combinations are readily comprehensible ; but the fact that 

 entirely new characters not possessed by the parents may appear in hybrids 

 is not explicable at the first glance. Thus Datura ferox x D. laevis has brown 

 stems and violet flowers, while both of the parent stocks have green stems 

 and white flowers. The hybrid between two races of Mirabilis Jalapa, one of 

 which possesses white and the other bright yellow flowers, is distinguished by 



