Variation occurring in Biscntella laevigata. 



23 



spond to one of the glabrous or intermediate grades. In the one 

 instance in which a plant not belonging to the extreme smooth type, 

 but with numerous marginal hairs, was crossed with a hairy form, 

 the general level of hairiness in the offspring was very considerably 

 higher. 



At the time of writing the character of the twenty-one hairy 

 plants was unchanged. The fifty-four plants bearing leaves with a 

 smooth, surface were still smooth, and the number of marginal hairs 

 was gradually becoming less. The remaining forty-five plants 

 originally bearing leaves with an intermediate surface were all 

 tending to become less hairy, in fact the leaf surface was free from 

 hairs in all those which had apparently reached the stationary 

 point.* 



A few experiments were also made with the view of determining 

 the character of the offspring in cases in which the parents resembled 

 one another in texture. To this end certain individuals were placed 

 under muslin covers, and either self-fertilised or crossed with others 

 of the same type. Unfortunately none of the plants that were 

 smooth set seed ; four hairy individuals of the Genevese stock, 

 however, fruited freely, and from them sixty plants were obtained, 

 all of which showed the same degree of hairiness as the parents. 

 It is of interest to compare these numbers with those obtained from 

 the two hairy plants A and B (see Table II), which were freely 

 exposed to insect visits ; in the case of the latter only about 80 per 

 cent, of the offspring belonged to the hairy type. 



Although the results tabulated in the preceding pages have been 

 obtained from observations upon a comparatively small number of 

 plants, they are, I think, sufficiently concordant to justify the follow- 

 ing conclusion. The experiments went to show that a blending of 

 parental characters as regards hairiness and smoothness occurs to a 

 certain extent in the offspring of plants of dissimilar types, giving 

 rise to intermediate forms. But this intermediate condition in 

 respect of hairiness is only found exceptionally among full-grown 

 individuals. For whereas in plants which at first are distinctly hairy, 

 the hairiness persists almost without exception, I have found that 

 in nearly every case those plants which as young seedlings present 

 an intermediate condition, assume, .as they grow older, a more dis- 

 tinctly glabrous habit. This change of character in the cross-bred 

 seedlings which are originally intermediate, takes place gradually ; 

 occasionally it does not occur until several leaves have been produced, 

 but more often it is apparent as soon as the second and third leaves 

 have developed. 



* Though the seeds were all sown together, they germinated at such unequal 

 intervals that the plants were at this time in very different stages of development. 



