LEGUMINOSAE 373 



or descending (Papilionatae). In many cases it is -|- to a high degree, 

 having a large petal posterior (vexillum or standard), two lateral 

 (alae or wings), and two anterior joined to form a keel or carina. 

 A typically of 10 sta., free or united into a tube; in the latter case 

 the tenth sta. (the posterior one) often remains free, so as to leave a 

 slit in the tube, only covered loosely by this sta. Many variations 

 are found. In cases where a keel is present, the sta. are enclosed 

 in it. G typically of one cpl. with its ventral side directly posterior; 

 long style and terminal stigma. There are two rows of ovules (alt. 

 with one another so as to stand in one vertical rank), anatr. or 

 amphitr., ascending or pend. 



Fertilisation (Papilionatae). The keel encloses the essential organs, 

 protecting them from rain, &c. and rendering the fl. complex. Honey 

 is secreted by the inner sides of the sta. near their base, and accu- 

 mulates in the stamen-tube round the base of the ovary. The tenth 

 sta. is free of the tube, and at the base, on either side of it, are two 

 openings leading to the honey. The honey is thus concealed and at 

 some depth, so that a clever insect with a tongue of moderate length 

 is required. All this points to the P. being bee-flowers (class H), as 

 in fact is the case. Insects alight upon the wings and depress them by 

 their weight, whilst they probe for honey under the standard. The 

 wings are always joined to the keel, usually by a protuberance in the 

 former fitting into a suitable hollow in the latter, so that the keel 

 is thus depressed likewise. This causes the emergence of the essential 

 organs, the stigma usu. coming first, so that a fair chance of cross- 

 fert. exists. Self-pollination usu. occurs when the insect flies off, 

 leaving the keel to return to its former position. 



"Four different types of structure may be distinguished (in Papi- 

 lionatae) according to the manner in which the pollen is applied to 

 the bee : (i) P. in which the sta. and stigma emerge from the carina 

 and again return within it. They admit repeated visits; e.g. Tri- 

 folium, Onobrychis. (i) P. whose essential organs are confined under 

 tension and explode. In these only one insect's visit is effective ; 

 e.g. Medicago, Genista, Ulex. (3) P. with a piston mechanism 

 which squeezes the pollen in small quantities out of the apex of the 

 carina, and not only permits but requires numerous insect visits; 

 e.g. Lotus, Ononis, Lupinus. (4) P. with a brush of hairs upon the 

 style which sweeps the pollen in small portions out of the apex of 

 the carina. They for the most part require repeated insect visits ; 

 e.g. Lathyrus, Vicia." (Miiller.) Cleistogamy is fairly common. In 

 several cases the stigma in the unvisited fl. lies in the keel among 

 the pollen, but it has been shown that it only becomes receptive 

 (if young) when rubbed, so that autogamy does not necessarily occur. 

 For the phenomenon of enantiostyly (right- and left-styled fls.) see 

 Cassia. Some have fls. which after fertilisation bury themselves in 

 the earth and there ripen their fruit; e.g. Arachis, Lathyrus, Trifolium, 

 Vicia, Voandzeia, &c. 



Fr. typically a legume, or pod opening by both sutures. In some 

 the pod is constricted between the seeds, forming a lomentum which 

 breaks up into indeh. one-seeded portions. The pods frequently open 

 explosively, the valves twisting up spirally, e.g. in Ulex, Cytisus sp., 



