4 

 MORPHOLOGY. 



The flowers of Astragalus are papilionaceous; the calyx tubular: 

 the stamens united below; and the petals five and clawed. The up- 

 per petal is the banner with a conspicuously expanded blade creased 

 in the middle lengthwise, generally with a white spot in the middle, 

 and with sides and tip variously reflexed, or tip often hooded and al- 

 ways notched. The two lateral petals are the wings and are nearly 

 always very oblique and mostly narrow, eared at base of blade where 

 they are inset in corresponding depressions in the keel blades. The 

 wing blades are parallel with the keel and one or the other or both 

 flare at tip, and are generally a little longer than the keel and shorter 

 than the banner, frequently the tips are incurved over the keel 

 tip, the sides are flat, convex, or concave to the keel. The tip always 

 has a rudimentary or more evident notch near the middle of the end. 

 This notch rarely extends deep enough to make lobes as in Oxytropis, 

 and only in A. calycosus is there a long hair-like tongue extending 

 from the notch as a third lobe. The two lower petals are in their 

 blades united along the lower edge forming a boat-shaped keel which 

 inclose the stamens. This is variously pointed and colored but rare- 

 ly is extended into a beak. 



The fruit is a normally single-celled pod. formed by a single 

 carpel leaf joined by the edges, the seeds being borne on the tips of 

 the carpel veins. The ventral suture corresponds to the junction 

 line of the edges of the leaf, the dorsal suture to the midrib of the 

 leaf. The ventral edges are 'oosely united and always separate at 

 maturity. As a rule the seed-bearing line is thickened, and only in 

 the Homalobi is it thin and nerve-like. The thicker is the wall of 

 the pod the thicker is the suture, becoming sometimes 2 mm. thick. 

 In the Inflati it is produced inwards as a thin wing along the 

 middle, and in other groups is often a thickened ridge within and 

 often raised and thickened or wnnged without. In addition the pod 

 is mostly variously grooved or silicate along one or both sutures. 

 The dorsal suture rarely splits at maturity, but in the Homalobi the 

 pod mostly falls off into two curling valves. In A. lonchocarpus the 

 pod at last flattens into a perfect leaf. In the Podo-sclerocarpi 

 the pod tends to split at both sutures at the base. In the Sar- 

 cocarpi and Argophylli the ventral suture opens a very little, often 

 not enough for the seeds to fall out and the pod becomes long after 

 maturity, as in the Inflati a papery ball blown far by the wind. 

 There are all degrees of differentiation in the dorsal suture from a 

 mere line in the Inflati and simpler forms to a dorsal groove 

 without thickening, to a raised line or thin wing as in the Alpini 

 without being double, then passing into a simple double fold in the 

 wall with or without united sides, and then into a special partition 

 complete or nearly so which is clearly double on dissection as is 

 seen so well in the Sarcocarpi, and A. lentiglnosus. 



On the character of the pods and flowers hang most of the species, 

 combined with vegetative characters, many species much alike in 

 pods differ in foliage and habit. 



