28 THE BOOK OF NATURE STUDY 



keel. The form of these petals and their relations to one another 

 require the most careful study. The standard widens out rather 

 suddenly from a short concave basal part. This basal region 

 is green in colour, as are the veins on the white expanded portion. 

 If the inner surface of the standard be looked at, two green ridges 

 formed by indentation of its outer surface will be seen converging 

 forwards, and further back in the middle line a short transverse 

 bulge of similar nature. The significance of these projections 

 will be apparent when the way in which the parts of the flower 

 fit together is considered. The wings stand within the standard 

 and one on either side of the keel. Each has a narrow stalk- 

 like part, which widens out into the white portion (Fig 8, 2). 

 The outer surface of the wing is irregular owing to certain depres- 

 sions. Just in front of the widening out of the wing, near its 

 upper margin, is a deep conical depression pointing downwards 

 and forwards (Fig. 8, 5, c') ; from the inside this appears as a 

 projection. In front of this within the upper margin is a longer 

 and shallower depression (Fig. 8, 5, d'}. To remove the wing it 

 has to be pulled with some force from the keel, against which 

 it fits closely. The keel (Fig. 8, i and 4) is formed of two petals, 

 the stalks of which are distinct ; but further forward the petals 

 are joined by their lower margins so as to form a boat-shaped 

 structure in which the stamens and pistil are enclosed. On the 

 outer surface of each half of the keel, just below its upper margin, 

 are two depressions, one just where the petal widens from the stalk 

 (Fig. 8, 4, c), the other farther forward (d). The two depressions 

 in the wing (c f and d'} correspond with and fit into these depres- 

 sions in the keel. Into the anterior grooves formed by the fitting 

 together of wings and keel at d, there fit also the two ridges (d,"} 

 on the inner face of the standard. The wings and keel are so 

 closely locked together that anything which depresses the wings 

 will depress the whole structure. 



The ten stamens are enclosed within the keel. The one to- 

 wards the back of the flower is separate from the others. Its 

 stalk is broad below, thin and cylindrical below the anther. The 

 stalks of the other nine are joined for half their length to form a 

 trough-like structure around the pistil. The upper portions of the 

 filaments bearing the yellow anthers are free (Fig. 8, 7). Within 



