320 CHAPTERS ON EVOLUTION. 



closed flowers are produced, in addition to the ordinary conspicuous 

 and, as we shall see, " cross " or insect-fertilised flowers. These 

 closed flowers have been named " cleistogamous " a term applied 

 by Kuhn in 1867. They are self-fertilised, and produce numerous, 

 seeds; and their occurrence in the same plant along with cross- 

 fertilised blossoms, may perhaps be best explained on the theory that, 

 whilst the ordinary and less fertile flowers will afford to the- plant 

 the advantages and benefits which accrue from " cross-fertilisation," 

 the " cleistogamous " flowers may be regarded as the normal means 

 for the ordinary increase of the race. What the flower loses in 

 variation by the sparing fertility of the cross-fertilised flowers, it may 

 gain in the number of seeds which the cleistogamous flowers pro- 

 duce. Cleistogamous flowers likewise tend to economise pollen. 

 Whilst 400 pollen-grains may serve the purpose of close or self- 

 fertilisation in Oxalis, or even 100 grains in some violets, three-and- 

 a-half million grains may be produced in the insect-fertilised flowers 

 of the peony, and many millions in the case of wind-fertilised 

 flowers, whose pollen, like that of the firs, has to be distributed over 

 immense areas of land. 



There appears, therefore, to be a proportion of plants in which 

 the existence of stamens and pistil in the same flower the normal 

 condition of matters in ordinary plants is meant to and does 

 secure the fertilisation of the ovules by the flower's own pollen. 

 Why, then, seeing that the presence of correlated stamens and pistils 

 in each flower appears to be a common condition of plant life, do 

 we assume that not self-fertilisation but the opposite process cross- 

 fertilisation is the rule of nature ? The reply to this query involves 

 more than one important consideration. Let us briefly endeavour 

 to find a convenient starting-point in the familiar flower which Peter 

 Bell despised, and which, to minds of utilitarian type amongst our- 

 selves, is but a primrose still, and " nothing more." 



If we study the structure of the primroses we may gather in a 

 bed of these flowers, it will be found that the blossoms obtained from 

 one set of plants will vary in certain respects from the flowers of the 

 other and neighbouring plants. There is no difference in appearance 

 or in outward aspect between the primroses, because the differences 

 referred to affect chiefly the position of the stamens and the length 

 of the style (or " neck " of the pistil) in each variety. But we may 

 readily discover that, selecting any one primrose plant, all the 

 flowers of that plant will be either long-styled (Fig. 208 A) or short- 

 styled (Fig. 208 B), and will not exhibit a mixture of the two 

 varieties. " The two kinds of flowers," says Mr. Darwin, speaking 

 of the long and short-styled cowslips, which form a closely allied 

 species to the primroses, " are never found on the same individual 

 plant ; " and he also remarks that he has never met with any 



