338 AUTOGAMY. 



which meanwhile have undergone dehiscence, are brought to the same level as the 

 stigma. Although the horizontal distance between the stigma and anthers is veiy 

 small, it is still Sufficient to prevent the stigma from becoming coated with pollen 

 from the anthers. Moreover, the stamens standing opposite the sepals incline out- 

 wards soon after, thus increasing perceptibly the distance between anthers and 

 stigma. Synchronously with the outward inclination of these stamens there is an 

 up-growth of those which stand in front of the petals, and here again the operation 

 takes place according to a definite law of succession, and continues until the anthers 

 .are raised to the height of the stigmas. These anthers, like the others, do not adhere 

 at first to the stigma, and it sometimes happens that the stigma remains unsupplied 

 with pollen even on the sixth day of flowering if none is brought by insects. But, 

 at last, on the seventh or eighth day some, if not all, the filaments move towards the 

 centre of the flower, and the pollen-covered anthers are pressed against the stigma, 

 which has not yet lost the power of receiving the pollen. Usually the five stamens 

 opposite the sepals act in the same manner, and all the ten anthers then ultimately 

 form a ring surrounding the stigma from which pollen may still be transferred by 

 insects to other flowers. The flowers of Saxifraga controversa are likewise proto- 

 .gynous, and adapted to cross-fertilization in the first period of flowering. Of the ten 

 .stamens, the first to elongate are the five opposite the sepals; the anthers borne at 

 their extremities ascend to the level of the stigma and during the process accomplish 

 their dehiscence. For a short time anthers and stigmas are separated by a small 

 interval of space, but soon afterwards the filaments incline a little towards the centre 

 and deposit pollen upon the stigmas. The five stamens in question then slope away 

 from the centre, and their empty and shrivelled anthers fall off. Meanwhile the 

 five stamens opposite the petals have grown up to the level of the stigmas and offer 

 3, fresh supply of pollen for dispersion. But this pollen cannot be used for autogamy 

 owing to the fact that the stigmas shrivel up after they receive the pollen of the first 

 five stamens, and are no longer capable of playing a part in fertilization. The 

 second supply of pollen can, therefore, only be appropriated to the fertilization of 

 younger fiowers through the instrumentality of insects. In other words, the five 

 anthers in front of the sepals devote their pollen to autogamy, whilst the five 

 opposite the petals devote theirs to cross-fertilization. 



As in these Saxifrages so also in Alsineae we find two whorls of stamens opposite 

 the sepals and petals respectively, and a certain general resemblance unmistakably 

 exists in the whole arrangement of the various parts of the flowers. The AlsineiB 

 that we here have to deal with are protandrous, and as examples may be taken 

 Gerastium longirostre, Malachivmi aquaticum, Sagina saxatilis, Spergula arvensis, 

 and Stellaria media. Dehiscence takes place in the anthers opposite the sepals 

 synchronously with the opening of the corolla, and the pollen exposed thereby is 

 available for cross-fertilization. At that period the styles are still coherent, and the 

 stigmatic tissue, which is composed of short transparent hairs, is inaccessible. Soon 

 afterwards, however, the styles part asunder, and the stigmatic tissue assumes such 

 a position as to ensure cross-fertilization in case insects bringing pollen from other 



