DIV. n 



SPERMATOPHYTA 



559 



impossible and favour cross-pollination. It is obvious that dioecism 

 completely prevents self-fertilisation, and that monoecism at least 



J. 



2. 



FIG. 531. Flower of Anthriscus sylvestris. Slightly magnified. 1, In the male, 

 2, in the female condition. (After H. MOLLER.) 



hinders the pollination of the flowers with pollen from the same plant. 

 A similar result is brought about when the two kinds of sexual organs 

 of a hermaphrodite flower mature at different 

 times. This very frequent condition is known 

 as DICHOGAMY. There are obviously two 

 possible cases of dichogamy. Either the 

 stamens mature first and the pollen is shed 

 before the stigmas of the same flower are 

 receptive ; the plant is known as PROTAX- 

 DROUS. On the other hand, the style with 

 its stigma may ripen first, before the pollen 

 is ready to be shed; the plant is PROTOGYNOUS. 

 PROTANDRY is the more frequent form 

 of dichogamy. It occurs in the flowers of the 

 Geraniaceae, Campanulaceae, Compositae, 

 Lobeliaceae, Umbelliferae (Fig. 531), Gerani- 

 aceae, Malvaceae (Fig. 664), etc. The anthers, 

 in this case, open and discharge their pollen 

 at a time when the stigmas of the same flowers 

 are still imperfectly developed and not ready 



for pollination. In Salda also (Fig. 525) FIG. 532. Inflorescence of Plan 



protandry is the necessary preliminary to the 

 cross-pollination. 



In the less frequent PROTOGYNY the female 

 sexual organs are ready for fertilisation before 

 the pollen of the same flowers is ripe, and 

 the stigma is usually pollinated and withered 



before the pollen is shed (Scrophularia nodosa, Aristolochia dematitis, 

 Helleborus, Magnolia., Plantago, Fig. 532). 



tago media with protogynous 

 flowers. The upper, still closed 

 flowers (9) have protruding 

 styles ; the lower ( $ ) have 

 lost their styles, and disclose 

 their elongated stamens. (After 

 F. NOLL.) 



