FRUITS AND SEEDS 239 



Fertilisation is dependent upon pollination, i.e., upon the 

 transference of pollen grains to the stigma of a similar 

 flower. Seeing that the gardener has in many cases, in order 

 to obtain seeds, to proceed to artificial pollination by transfer- 

 ring, with the aid of a fine brush, the pollen to the stigmatic 

 surface, we may point out that there are many hindrances 

 to this method of procedure. In nature, too, we may often 

 observe that the pollen from opening stamens may fall upon 

 the stigma of the same flower (self-pollination) but remains 

 without effect. This is the case in so called dichogamous flowers, 

 in which the two kinds of sexual organs ripen at different times. 

 In some cases the anthers ripen and disperse their pollen before 

 the stigma of the flower is receptive. Such plants are termed 

 protandrous (Geraniaceae, Malvacete, Compositse, &c.), and fer- 

 tilisation can only be effected with the aid of a second, younger 

 flower, by either natural or artificial means. In the reverse 

 case, namely, in that of the protogynous flowers, the stigma 

 which ripens before the stamens requires to be fertilised with 

 pollen from an older flower, because its stamens are as yet not 

 fully developed (some Graminea3). But even in the case of 

 both sexual organs developing at the same time, self-pollination 

 may often be difficult, if not impossible, because the stamens 

 are not long enough to reach the stigma. This is the case 

 with dimopphie flowers. In this case a plant will develop 

 hermaphrodite flowers of two kinds (Primrose). Some speci- 

 mens liave a long style, so that the stigma will reach to the 

 top of the corolla tube {pin-cijed). The stamens, however, 

 will be short, and remain hidden within the tube of the 

 corolla. In other specimens the reverse will be the case 

 (Jieterostyly). 



Nature seems here to point out the way in which fertilisation 

 is to be effected. The flowers with long stamens are intended 

 to pollinate the long-styled forms. That this course of pollina- 

 tion is attained with good results has been proved experi- 

 mentally by Darwin. He found that the production of 

 seed is small, or sometimes even nil, when one (short or long- 

 styled) form is pollinated with its own pollen, or with pollen 

 from a similar flower, but that a large production of seed 

 results from the pollination of a long-styled form with pollen 



