I270 A TEXTBOOK OF THEORETICAL BOTANY 



The following exceptional cases should be noted as modifications of the 

 general scheme. 



1. Some individuals hermaphrodite, others with both male and female 

 flowers. CaUitriche. 



2. Some individuals male, others with both male and female flowers. 

 Arctopiis (Umbelliferae). 



3. Some individuals female, others with both male and female flowers. 

 Moms. 



4. Some individuals female, others with both male and hermaphrodite 

 flowers. Gleditschia. 



STATUS OF FLOWERS WITH REGARD TO POLLINATION 



The classification of the sexual conditions of flowers as originally pre- 

 sented by Errera and Gevaert had the disadvantage of bringing together in 

 one scheme, both structural differences and behavioural differences, which 

 led to complication and some lack of clarity. We have attempted here to 

 separate the two ideas. We have presented the scheme of structural differ- 

 ences above and we must now consider differences of sexual behaviour in 

 regard to pollination. The following scheme is based mainly on that of 

 Errera, but with some modifications, to avoid, so far as possible, the over- 

 lapping of groups. 



\. Cleistogamy (Kuhn). Flowers do not open and are internally self- 

 pollinated or self- fertilized. This condition will be more fully considered 

 later. 



IL Chasmogamy (Axell). Flowers are pollinated in the open condition. 



1. Autogamy (Delpino). Homogamy (Sprengel). Self-pollination. 

 This is naturally only possible in hermaphrodite flowers. It is only 

 effective if the species is self- fertile, e.g., TrifoUum arvense. If the 

 species is self-sterile, e.g., TrifoUum pratense, autogamy is ineffective 

 and cross-pollination must occur. The mode of autogamy has 

 been distinguished as: 



A. Direct autogamy. Pollen deposited directly from the anthers 

 on to the receptive stigma. 



B. Indirect autogamy. Pollen has to be conveyed to the stigma by an 

 external agent. 



2. Allogamy (Kerner). Cross-pollination, by pollen from another 

 flower of the same species. This may happen in either of two ways : 

 Geitonogamy (Kerner), which implies pollination by another flower 

 of the same inflorescence or the same plant. Xenogamy (Kerner), 

 which impHes pollination from another individual. Either of these 

 events may occur in unisexual or in hermaphrodite flowers, but in 

 the latter, allogamy requires that there shall be some means of avoid- 

 ing primary self-pollination. This is secured by one of two methods : 



