1917.] Observations on Pollination in Alysicarpus. 289 



to the stigma, but fertilisation does not take place without an 

 explosion caused by the visit of particular insect mentioned. 



The flowers appear to be self -sterile, for T selfed 6 flowers 

 and bagged them, but none of them set. It is however evident 

 that these results are by no means conclusive, for self-sterility 

 is a character that is not constant l for all individuals of the 

 same species, but varies with the locality and the individuals. 

 The flowers in this species are thus adapted only for cross 

 fertilisation, and probably it is for the purpose of giving the 

 plant enough chances, that one or two flowers only are ready 

 for pollination every day on any inflorescence. 



Now let us see how cross fertilisation takes place. In an 

 open flower a state of tension exists between the ovary and the 

 keel, as in Indigofera a ; and as already mentioned, the keel 

 constitutes a spring which presses the ovary downwards, and is 

 kept in position by means of the various folds of the wings 

 and keel as described above. 



It therefore follows that when the insect (Nomia oxy- 

 beloides) alights on the flower resting with its limbs on the wings, 

 which are interlocked with the keel, and thrusts its head under 

 the standard, the folds of the wings and the keel slip down the 

 staminal column enclosing the ovary. At the same time the 

 keel splits open above from base to tip. When the splitting 

 has extended as far as the end of the style, the stretched parts 

 suddenly separate and the keel with its interlocked wings 

 spring down owing to the bending of the claws above 

 referred to till they are nearly at right angles to the ovary 

 which has jerked suddenl v upwards. . 



The narrowness of the keel just below the apex which 

 holds the staminal column slightly inwards, and the cupular 

 tip of the keel which holds the staminal tip slightly downwards, 

 are responsible for the strong jerk given to the tip ot the 

 already jerked stamin I column. The pollen is thereby thrown : 

 upw rds and deposited on the ventral surface ot the ^ insect 

 with great force. At the same time the slightly projecting 

 stigma conies into contact with the ventral surface ot the 

 insect, which is covered with foreign pollen, if the insect 

 happens to have previously visited another flower of the same 

 secies. In this way the stigma is cross-polhnated. Since the 

 throwing of the pollen precedes the touching of t he * t JM 

 occurs simultaneously, there is a fear of the pollen of ttosame 

 flower being deposited on the stigma, and in such cases the 

 foreign pollen alwavs predominates. 8 , 



u Before proceeding further I may here relate .a few other 

 observations conned ed with the pollination in A. rugosus. 



1 Knuth's Handbook of Flower Pollination, vol. I, page 196. 



2 " The Improvement of Indigo ", Howards. 

 8 Knuth's Pollination, vol. I, page 36. 



