150 LEGUMINOUS FLOWER [CH. 



stands up more or less, and is termed the standard (Vexil- 

 lum) : in the bud this is folded together with its margins 

 directed downwards and covering all the other petals. 



Then come two narrower petals, one on each side and 

 pointing forwards, termed the wings (Alee); and these 

 cover with their lower margins the two lowermost petals 

 in the bud, their upper margins being overlapped by the 

 lower margins of the folded standard. 



Finally there are two narrow petals, each shaped 

 somewhat like the sides of a boat cut vertically along 

 its longitudinal axis, and since these two petals fit edge 

 to edge as if the bisected boat were reconstructed by 

 bringing together its two halves they form what is 

 known as the keel (Carina): in the bud these two 

 opposed carinal petals have their upper margins over- 

 lapped by the wings. 



The separate insertions of these five unequal petals 

 alternate with the sepals. 



Just inside the petals come the ten stamens, and it is 

 a curious fact that in all the cases here concerned the 

 filaments are conjoined into a tube surrounding the ovary: 

 in Ulex, Genista and Cytisus this tube is complete, but in 

 Robinia the tenth (posterior) stamen stands alone, the 

 other nine forming the tube. 



The ovary is formed of a single carpel, the apex of 

 which is prolonged into a style. 



The Leguminous type of flower is thus seen to be 

 pentamerous and diplostemonous, zygomorphic in the 

 median plane, with a gamosepalous calyx, perigynous 

 free petals, and mon- or di-adelphous stamens, and a 

 single free carpel ripening to a pod. 



This may be expressed in a floral formula as follows : 



|#(5) Co, Ao + o [or 5 + 4 + 1] 01. 



