APPENDIX A 



647 



in Lamium, but, as the mechanism is more precise, sufficient probability of 

 pollination can be secured with greater economy of pollen than in other Labi- 

 atae (Fig. 497). Only the two obliquely anterior stamens are matured, the 

 posterior are represented by minute staminodes, or are quite abortive. The 

 anthers of the two well-developed stamens have the " connectives " between 

 the anther-lobes elongated, so that they are separated by about half an inch. 

 Each anther is affixed midway on the short stout filament of the stamen by 

 a flexible joint, so as to be able to move like the lever of an Egyptian well. 

 One of the lobes is directed forwards, and this develops normal pollen ; 

 the other is directed backwards and develops as a sterile knob. This is so 

 placed as to block the entrance to the corolla-tube, while the fertile lobe rests 



Fig. 497. 



Pollination of Salvia pratensis. i, Flower visited by Humble Bee, showing the 

 projection of the curved connective from the helmet-shaped upper lip, and the deposit 

 of the pollen on the back of the Bee. 2, older flower, with connective withdrawn 

 and elongated style. 4, the staminal apparatus at rest, with connective enclosed 

 within the upper lip. 3, the same when disturbed by the entrance of the proboscis 

 of the Bee in the direction of the arrow. /= filament. c = connective. s = the 

 obstructing half of the anther, which produces no pollen. (After Strasburger.) 



under the hood of the corolla. The flower is strongly protandrous, the 

 style being hidden, and the stigma-lobes appressed at the time of shedding 

 of the pollen. 



If a large insect, perching on the lower lip of the flower of Salvia, inserts its 

 proboscis, the sterile lobes will be pressed upwards, and this will cause the 

 fertile lobes to descend, depositing the pollen over a definite area of the insect's 

 back. In older flowers that have already shed their pollen, the style elongates : 

 its lobes diverge and take such a position that the stigma touches that region 

 of the insect's body which received the pollen from the younger flowers. 

 Cross-pollination thus follows on repeated visits to flowers of various ages ; 

 and it is effected with a high degree of certainty, though in each flower only 

 two half-anthers are fertile. Economy of pollen follows on perfection of the 

 mechanism. 



ORDER : SYNANDRAE. 

 Family : Compositae. Examples : Ox-Eye, Dandelion, Cornflower. 



The Family of the Compositae consists mostly of herbs. It is of world- 

 wide distribution, and is the largest Family of Flowering Plants. It is char- 

 acterised by having the gamopetalous flowers collected into capitula, or heads. 



