Chap. XVI. 



THE CROSSING OF VARIETIES. 



87 



it is highly remarkable, and is established on excellent evidence. 

 Kolreuter minutely describes five varieties of the common tobacco, 25 

 which were reciprocally crossed, and the offspring were intermediate 

 in character and as fertile as their parents : from this fact Kolreuter 

 inferred that they are really varieties ; and no one, as far as I can 

 discover, seems to have doubted that such is the case. He also 

 crossed reciprocally these five varieties with N. glutinosa, and they 

 yielded very sterile hybrids; but those raised from the var. perennis, 

 whether used as the father or mother plant, were not so sterile as 

 the hybrids from the four other varieties. 26 So that the sexual 

 capacity of this one variety has certainly been in some degree 

 modified, so as to approach in nature that of N. glutinosa. 21 



These facts with respect to plants show that in some few 

 cases certain varieties have had their sexual powers so far 

 modified, that they cross together less readily and yield less 

 seed than other varieties of the same species. We shall 

 presently see that the sexual functions of most animals and 

 plants are eminently liable to be affected by the conditions 

 of life to which they are exposed ; and hereafter we shall 



23 ' Zweite Forts.,' s. 53, namely, 

 Nicotiana major vulgaris; (2) peren- 

 nis ; (3) transylvanica ; (4) a sub- 

 var. of the last ; (5) major latifol. fl. 

 alb. 



26 Kolreuter was so much struck 

 with this fact that he suspected that 

 a little pollen of N. glutinosa in one 

 of his experiments might have acci- 

 dentally got mingled with that of 

 var. perennis, and thus aided its fer- 

 tilising power. But we now know 

 conclusively from Gartner (' Bastar- 

 derz.,' s. 34, 43) that the pollen of 

 two species never acts conjointly on a 

 third species ; still less will the pollen 

 of a distinct species, mingled with a 

 plant's own pollen, if the latter be 

 present in sufficient quantity, have 

 any effect. The sole effect of mingling 

 two kinds of polle-n is to produce in 

 the same capsule seeds which yield 

 plants, some taking after the one and 

 some after the other parent. 



27 Mr. Scott has made some obser- 

 vations on the absolute sterility of a 

 purple and white primrose (Primula 

 vulgaris) when fertilised by pollen 

 from the common primrose ('Journal 



of Proc. of Linn. Soc.,' vol. viii., 1864, 

 p. 98) ; but these observations require 

 confirmation. I raised a number of 

 purple-flowered long-styled seedlings 

 from seed kindly sent me by Mr. 

 Scott, and, though they were all in 

 some degree sterile, they were much 

 more fertile with pollen taken from 

 the common primrose than with their 

 own pollen. Mr. Scott has likewise 

 described a red equal-styled cowslip 

 (P. veris, ibid. p. 106), which was 

 found by him to be highly sterile 

 when crossed with the common cow- 

 slip ; but this was not the case with 

 several equal - styled red seedlings 

 raised by me from his plant. This 

 variety of the cowslip presents the 

 remarkable peculiarity of combining 

 male organs in every respect like 

 those of the short-styled form, with 

 female organs resembling in function 

 and partly in structure those of the 

 long-styled form ; so that we have 

 the singular anomaly of the two 

 forms combined in the same flower. 

 Hence it is not surprising that these 

 flowers should be spontaneously self- 

 fertile in a high degree. 



