CHARLES DAB WIN. 167 



mission, which may be confined to one sex, or be common to both 

 sexes of the prepotent form. Fourthly, transmission hmited by sex, 

 generally to the same sex in which the inherited character first ap- 

 peared. Fifthly, inheritance at corresponding periods of life, with 

 some tendency to the earlier development of inherited character." 



The phenomena connected with fertilisation are discussed chiefly 

 in ' The various Contrivances by which Orchids are fertilised by 

 Insects' (1862), ' The Effects of Cross and Self Fertilisation in the 

 Vegetable Kingdom' (1876), and ' The Different Forms of Flowers 

 on Plants of the same Species' (1877). The chief result of Mr. 

 Darwin's observations is, as is well known, the conclusion that 

 while self-fertilisation is, in most cases, possible, there is invariably 

 provision either for habitual or for occasional self- fertilisation, 

 without which the race would gradually and surely deteriorate : 

 "Nature telling us," says Mr. Darwin, "in the most emphatic 

 manner, that she abhors perpetual cross-fertilisation." In the 

 family of OrchidacecB, in particular, he points out that in certain 

 species the pollen is not only inoperative, but is actually poisonous 

 to the stigma of the same flower ; and that in many the con- 

 trivances and adaptations for cross-fertilisation are of the most 

 complex and beautiful nature. In the second of the three volumes, 

 named above, Mr. Darwin advocates the view that this preference 

 for cross-fertilisation is not the result of any inherent dislike of 

 Nature to a union between near relatives ; the advantage obtained 

 by crossing " depends on the individuals which are crossed differing 

 slightly in constitution, owing to their progenitors having been 

 subjected during several generations to slightly different conditions, 

 or to what we call in our ignorance spontaneous variation. This 

 conclusion," Mr. Darwin says, " is closely connected with various 

 important physiological problems, such as the benefit derived from 

 slight changes in the conditions of life, and thus stands in the 

 closest connection with life itself. It throws light on the origin of 

 the two sexes, and on their separation or union in the same indivi- 

 dual, and lastly on the whole subject of hybridism." 



In the last-named work Mr. Darwin treats of cleistogamic 

 flowers, which he regards as modified and degraded in order to 

 afford an abundant supply of seeds with little expenditure. Species 

 with cleistogamic flowers always produce also perfect flowers, so as 

 to allow of occasional cross-fertilisation. Contrary to the opinion 

 of some authorities, Mr. Darwin regards hermaphrodite as the 

 primitive condition of flowers ; unisexuality as a degraded type, in 

 which, owing to changed conditions, the production of a great 

 number of seeds has become superfluous ; and an economy of vital 

 powers is then introduced, resulting from the same flower not 

 bearing both male and female organs. 



The singular i)henonema connected with the growth of climbing 

 plants were the subject of a paper presented to the Linnean Society 

 by Mr. Darwin in 1865. An immense mass of observations on 

 this subject was contained in his 'Movements and Habits of 

 Climbing Plants' (1875), which were extended to similar pheno- 

 mena in the vegetable kingdom generally in the ' Power of Movement 



