PAPILIONACE^. 95 



this is the usual type of fruit : but in some the pod breaks 

 up transversely into a number of one-seeded sections, 

 which may open or not ; and in a few genera there is 

 only one seed and the pod does not open. 



Exceptions to the above are that in the common, introduced Gorse, 

 ULEX, the calyx is coloured yellow and divided deeply into two parts ; and 

 that in sophora the keel petals are hardly united, and the stamens are all 

 free. Otherwise the flowers are all made on this plan. There are small 

 individual differences, which serve to distinguish the genera. In the 

 Rattle-pods, crotalatiia, and the introduced Gorse and Broom, the 

 anthers are small alternately short and attached lightly by the middle of 

 the back (versatile) or long and fixed firmly at the base : in the Beans, 

 Phaseolus, the keel and its enclosed stamens and style, are remarkably 

 long and curled up into a complete spiral. In some genera the keel 

 is sharp-pointed, in others blunt ; in dum asia is joined more or less firmly 

 at the back to the wing petals. In some the style is hairy all round ; in 

 others only on the upper-side ; in others again it has no hairs ; and in one 

 genus, dumasia, it has a thickening just at the bend. These differences 

 only serve to show the essential similarity of the flowers. Greater and 

 more useful differences occur in the leaves. These may be simple, as in 

 crotalaria, or composed of leaflets : either three only, all equally stalked 

 {digitate) or with the central stalk longer {pinuately trifoliate) ; or several, 

 either an even number, or an odd number, (i.e.), in pairs with one at the 

 end ; or as in the Vetch with a tendril at the end. It is chiefly by these 

 differences that the family is divided into sections (tribes). 



In all the papilionace^ the base of the leaf-stalk (or if 

 that is very short as with most leaflets, the whole of it), is 

 swollen, and so constructed as to be capable of bending up 

 or down, and by doing so changes the position of the blade 

 morning and evening : sp that while by day the blade is more or 

 less horizontal, at night it becomes more or less vertical. The 

 evening movement is in some cases upwards, in others down ; 

 and often brings the blades not only vertical but also with the 

 upper sides of adjacent leaflets together : and sometimes the 

 leaflet is folded along the midrib with the same effect. It 

 is a protective movement designed to prevent loss of heat by 

 radiation to the sky, and is shared, but to a much smaller 

 extent, by a number of other plants. Attention is here called 

 to it because it is one which one can hardly help noticing if 

 out after dark. 



The PAPiLiONACE^ show interesting adaptations to the 

 visits of insects to their flowers. In some cases the simple 

 weight of the insect pressing the keel petals down, brings the 

 anthers into contact with its body. In flowers with sharp 

 pointed keel pollen is shed previously out of the anthers and 

 when a heavy insect, such as a bee, alights on the keel, is 

 pushed out by the style. This is the purpose of the hairs 

 below or round the stigma. More advanced still is their 



