1830 A TEXTBOOK OF THEORETICAL BOTANY 



small-flowered species self-pollination may become the rule. They all 

 contain nectar, which is secreted from nectaries developed at the base of 

 the stamens. The flowers are mostly protandrous and the greater the 

 prospect of insect visits the more marked is the dichogamy. In addition 

 to the large hermaphrodite flowers there are small female ones developed 

 in some species. 



In Geranium pahistre the flowers are markedly protandrous and the 

 nectar is secreted by glands at the bases of the five inner stamens. Nectar 

 guides are present on the petals, while hairs at their bases prevent rain- 

 drops from reaching the nectar. The five inner stamens ripen first and then 

 the five outer ones. Only when all ten have shed their pollen do the stigmas 

 mature for previously they have been tightly closed together, but now they 

 open out and project from the centre of the flower. After dehiscing, the 

 stamens all bend outwards so far that self-pollination is impossible. The 

 condition in G. pratense is the same. 



In Geranium pyrenaicum the nectar is enclosed in glands at the bases of the 

 five outer stamens. These stamens grow up first, overtopping the immature 

 stigmas, and the anthers turn outwards and dehisce. At this stage the five 

 inner stamens curve downwards so that their anthers are well out of the 

 way of visiting insects. A day later the inner stamens grow up and dehisce 

 so that the closed styles are now surrounded by all ten stamens which are 

 hberating ripe pollen. A day or two later the stigmas begin to separate and 

 they open out to He level with the anthers. Hence if all the pollen has not 

 been removed by insects, self-pollination is now possible, and is as likely 

 as cross-pollination. If on the other hand insect visits have been numerous 

 all the pollen will have already been removed and cross-pollination 

 rendered certain. 



In Geranium molle the stigmas are, as usual, closely pressed together in 

 the centre of the flower and the anthers closed and arranged outside the 

 stigmas. This condition is followed by the incurving of the outer whorls of 

 stamens, which bend in towards the centre of the flower and lie over the 

 immature stigmas. Even before these anthers have dehisced, however, 

 the stigmas begin to grow up and expand between the stamens so that self- 

 pollination becomes possible. At this stage the inner stamens begin to 

 curve inwards and the anthers dehisce. Hence at this stage an insect 

 visiting the flower touches the anthers and stigmas at the same time and 

 can achieve cross-pollination or self-pollination equally easily. 



Finally in Geranium pusillum only the five stamens which alternate with 

 the petals bear anthers and are provided with basal nectaries. When the 

 flower opens the stamens are all erect and before the anthers split, the 

 five styles have opened out between them. Hence, at this stage the flower 

 is essentially female, but soon after^the anthers split and the stigmas spread 

 out further, so that they are almost inevitably dusted with pollen as it is shed. 

 Finally the anthers bend over till they touch the stigmas. At this stage 

 pollen may be received by a visiting insect, but if the flower was not cross- 

 pollinated before its anthers matured, self-pollination is certain. 



