324 THE CROSSING OF FLOWERS. 



agrees with Sanicula in having hermaphrodite and staminate flowers in each 

 umbel, the hermaphrodite flowers developing first and being protogynous, so that 

 again the sticky stigmas of the first-opened flowers in a given locality can only be 

 fertilized by the pollen of other species. Later, the stigmas of the hermaphrodite 

 flowers separate, and to a certain extent offer themselves to the pollen of the neigh- 

 bouring staminate flowers which is now being shed. Laserpitium exhibits the 

 same general arrangement of flowers as Sanicula and Astrantia, but the herma- 

 phrodite flowers in the large, loose umbel are protandrous instead of protogynous. 

 Geitonogamy, however, obtains, just as in Astrantia, by the stigmas at the top of 

 the divided style exposing themselves to the pollen from the anthers of the neigh- 

 bouring staminate flowers. Since the protandrous hermaphrodite flowers open 

 before the staminate ones, their stigmas are mature exactly at the same time that 

 the anthers of the latter shed their pollen. 



A notable exception to these Umbelliferse which have been described, where the 

 stigmas of one flower obtain the pollen from neighbouring flowers by the elongation 

 and bending of their styles into their neighbour's domain, thus producing geitono- 

 gamy, is aftbrded by others whose styles and stigmas retain their original position. 

 The stamens, however, elongate and straighten, and assume such a position that 

 the pollen liberated from their anthers can reach the stigmas of the neighbouring 

 flowers. One group of such species, of which Pachypleurum, so abundant on the 

 mountain heights of Europe, may serve as a type, develops a single flat umbel at 

 the end of the stalk bearing flowers all hermaphrodite. They are also protogynous 

 — their sticky stigmas can receive pollen, while their anthers are still closed. When 

 flowering first begins, therefore, crossing can only be with other plants. Then the 

 stamens straighten and stand out on all sides like a star till the long filaments place 

 their anthers in the line of the neighbouring flowers. Since the stigmas are still 

 receptive some of the pollen falling out of the bursting anthers inevitably reaches 

 the stigmas of one of these flowers. The process which occurs in the umbel of 

 Siler is but sliglitly different, although the flowers are exclusively protandrous, and 

 not protogynous like those of Pachypleurwvi. In spite of this difference in the 

 times of maturation the end attained is the same, as we shall see. The flowers in 

 an umbel of Siler do not mature simultaneously like those of Pachypleurum, but 

 the development proceeds very gradually from the circumference towards the centre 

 of the umbel, so that the anthers of the central flowers do not dehisce until the 

 outer ones have lost their pollen and matured their stigmas. Some of the crumb- 

 ling pollen which falls out of the shrivelling anthers is now deposited on these 

 ripening stigmas, since the thread-like filaments are long enough to reach to the 

 middle of the outer flowers, and thus geitonogamy almost invariably ensues. 



Both Pachypleurum and Siler and all the UmbelliferiB typified by them 

 contain only hermaphrodite flowers in their umbels, and in this respect they differ 

 from species of Athamanta, Spignel (Meum), and Chervil (Ghairophyllum, see 

 figs. 294 ^ and 294 *, p. 320), whose umbels contain both hermaphrodite and stami- 

 nate flowers like those of Astrantia and Sanicula. But this arrangement of the 



