1672 



A TEXTBOOK OF THEORETICAL BOTANY 



of species, has spread from the Mediterranean northwards into central 

 Europe, though several species occur in other parts of the world. The 

 genus Medicago is more widely distributed. There are about fifty species 

 occurring in Europe, Asia and North Africa. M. sativa (Lucerne) is an 

 eastern Mediterranean plant which is extensively cultivated, particularly in 

 America, as a fodder crop. It is interesting to note that for successful 

 growth in new areas the seeds must be inoculated with the appropriate 

 strain of nodule bacteria. Meltlotus, with twenty species, occurs in temperate 

 and subtropical parts of the Old World. Finally there is the large genus 

 TrifoUum with about 290 species, which occur chiefly in the north temperate 

 zone, though a few species are found in more southern mountainous 

 regions. Several species are cultivated, of which TrifoUum pratense var. 

 sativum and T. incarriatum are the most important. In Britain T. repens is 

 very valuable as a source of nectar for hive bees. 



Fig. 1529. — TrifoUiuu repens. A, Flower from 

 above after removal of calyx and standard 

 petal. B, T. pratense. Carina of flower 

 after depressal showing emergence of 

 stamens and stigma. {After Kniith.) 



As will be gathered, these flowers (Fig. 1529) possess nectar and 

 the pollination mechanism is relatively simple. The nectar is secreted 

 on the inner side of the base of the staminal tube. Since the calyx tube 

 is short, even short-tongued insects can reach the nectar. The wing 

 petals are partly fused with those of the keel and the whole moves upwards 

 and forwards together, but the depression is facilitated by very slender 

 claws which are fused for the most part to the staminal tube. The closing 

 ot the flower is brought about by the claws of the standard, which grasp the 

 other petals as well as the stamens, and by their elasticity guide them back 

 into place when the pressure exerted by the visiting insect is removed. To 

 reach the nectar the insect must thrust its head below the standard and 

 owing to the small size of the keel it has only the wing petals to support it. 

 These, together with the keel, are consequently depressed and the stamens 

 and stigma protrude from the keel. Since the stigma projects well beyond 

 the anthers, it touches the insect first and consequently cross-pollination is 



