THE DICOTYLEDONES 1673 



made sure. Only bees are able to work the mechanism successfully. This 

 species is apparently entirely self-sterile and in the absence of insect visits 

 no viable seed is produced. 



The Lotoideae are also quite a small sub-family of eight genera. Lotus 

 itself has about fifteen species mostly in temperate Europe and Asia. 

 Anthyllis with thirty species occurs in Europe, North Africa and Asia, while 

 Hosackia with thirty species is found in western North America. 



The pollination mechanism in Lotus is somewhat different from those so 

 far described and is based upon a pumping system. In Lotus corniculatus 

 (Fig. 1530) nectar is secreted as usual at the base of the stamen tube. The 

 wing petals possess deep depressions near the base of the limb, which fit 



Fig. 1530. — Lotus corniculatus. A, 

 Flower from the side after re- 

 moval of one wing petal. B, 

 Androecium and style in posi- 

 tion immediately after removal 

 of the pollen. {After Knuth.) 



into corresponding pits in the upper ends of the keel. Immediately behind 

 this point the wing petals are fused together so that when a suitable insect 

 visits the flower the wings and keel are simultaneously depressed. In the 

 bud the ten anthers discharge their pollen into the tip of the keel and then 

 shrivel up. As the flower grows the filaments of the five outer stamens 

 elongate, and their ends thicken and shut off the tip of the keel forming a 

 pollen chamber. This conceals the stigma and there is a slit along its upper 

 margin. When the keel is depressed the filaments are thrust further into the 

 keel and push out pollen through the slit. As pressure continues the stigma 

 is also protruded so that either cross-pollination or self-pollination may 

 take place. The latter however is ineffective because the stigmatic surface 

 must be rubbed before it is receptive and this can only happen when it is 

 touched by a visiting insect. 



When we pass to the next sub-family, the Galegoideae, we find a much 

 larger assemblage of nearly seventy genera, arranged in a number of 

 distinct tribes. Several of the genera are important. Indigofera is a large 



