310 



BOTANY 



MONCECIOUS plants (other Mucorineae, Algae, species of Carer, liicinus, 

 Box, Coniferae, Cupuliferae, etc.) the male and female organs occur 

 on different flowers, but the flowers are borne on the same plants. 

 The fertilisation between different flowers is thus secured ; but even 

 here crossing with other individuals is, for the most part, assured by 

 dichogamy. 



The term DICHOGAMY is used to denote the fact that the male and female sexual 

 organs attain their maturity at different times. When either the male or female 

 sexual organ matures before the other, the self-pollination of morphologically 

 hermaphrodite flowers is avoided and crossing ensured. Both hermaphrodism and 

 moncecism are more advantageous than dicecism, as 

 all the individual plants in such cases are able to 

 produce seeds ; while in dioecious plants the male 

 flowers cannot be utilised for the direct production of 

 seeds. Dichogamy secures crossing in such a simple 

 Tiianner. and is so easily attained by hermaphrodite 

 plants, that it is of very general occurrence in the 

 vegetable kingdom. According to the priority of the 

 maturity of their sexual organs, plants are designated 



PROTANDHOUS or PROTOGYNOU8. 



PROTANDRY, the earlier maturing of the male 

 sexual organs, is the more frequent form of dichogamy. 

 It occurs in the flowers of the Geraniaceae, Campanu- 

 laceae, Compositae, Lobeliaceae, Umbelliferae, Mal- 

 vaceae, etc. The anthers, in this case, open and dis- 

 charge their pollen at a time when the stigmas 

 of the same flowers are still imperfectly developed 

 and not ready for pollination. Accordingly, PKO- 



TANDROUS FLOWEKS CAN ONLY BE FERTILISED BY THE 

 POLLEN OF YOUNGER FLOWERS. 



FIG. 241. Inflorescence of Plan- In the less frequent PROTOGYNY the female sexual 

 tago media with protogynous organs are ready for fertilisation before the pollen 

 flowers. The upper, still closed o f the same flowers is ripe, and the' stigma is usually 

 flowers (?) have protruding uinated and wit hered before the pollen is shed ; so 

 styles; the lower (<?) have r 



lost th.-ir styles, and disclose tnat the PROTOGYNOUS FLOWERS MUST BE FERTILISED 

 their elongated stain. MIS. BY THE POLLEN OF OLDER FLOWERS (Anthoxanthum 



odoratum, Luzula pilosa, Scrophularia nodosa, Aris- 

 tolochia clematitis, Helleborus, Magnolia, Plantago, Fig. 241). 



A still more complicated method of effecting cross -fertilisation, because in- 

 volving also morphological and anatomical differences of structure, results from 

 HETEROSTYLY, or the peculiarity of some species of plants of producing stigmas 

 and anthers which vary in height in different individuals of the same species. 

 In contrast to the unlimited possibility of crossing in other hermaphrodite 

 flowers (panmixia), there is here a limitation to certain classes of individuals of 

 the species. A good example of heterostyled flowers is afforded by the Chinese 

 Primrose (Fig. 242). This plant has two forms of flowers, long-styled (L) and 

 short-styled (K), while the positions of the stigmas and anthers in the two kinds 

 of flowers are exactly reversed. The pollen grains of the short-styled flowers, 

 moreover, are larger, and the stigmatic papillae shorter, than in those with the 

 longer styles (p, P, and n, N). The purpose of such morphological and anatomical 



