1 68 THE PLANT WORLD. 



leaves, as is true of the Legnmiiiosae in general, are capable of 

 "■ sleep " movenients. the leaflets of the third order folding to- 

 gether upwardl}' upon the approach of night. When the leaves 

 wither and fall away the pinna as a whole separates from the 

 main, though very small, rachis, the pinnules sometimes remain- 

 ing attached but usually falling away separately. The tapering 

 twigs are. when young, slightly pubescent and as they mature 

 their ends develop into thorns. On account of the tapering form 

 of the numerous twigs, and their whip-like flexibility, the tree 

 has an exceedingly graceful form. Its delicate evergreen hue 

 always gives its habitat a note of color, even during the driest 

 seasons of the year when most, if not all. of the remaining vege- 

 tation has become more or less neutral in tint. 



The flowers, which are borne in great numbers, are almost radi- 

 ally symmetrical, the only evidence that the flower is of the type of 

 the Leguminosae being seen in the vexillum or upper petal, which 

 is of a somewhat different form from the rest, being supplied with 

 a longer claw, and white in color, while the rest are light, lemon 

 yellow. The presence of the white petal is sufficient to modify 

 the total color of the flower masses into a rather pale, greenish 

 yellow, distinguishing it at once by this feature alone from the 

 other species. The dorsiventrality of the flower is also marked 

 by the unequal stamens and by their position, and also by the 

 form of the pod, which of course is cjuite true to the family type. 

 As soon as the insect life in the desert is set in motion by the 

 rising sun the flowers are visited by myriads of insects of all 

 kinds, so that as one stands near a tree their buzzing is very 

 loud. The fruit, which develops rapidly during the early sum- 

 mer, consists of a papery pod bearing from one seed to a half 

 dozen, each one of which is separated from its neighbor by a 

 marked constriction of the pod, which at its outer end is con- 

 tinued into a slightly curved, rather long beak. The whole of the 

 pod when ripe splits into two layers, the inner of which consists 

 of a narrow strap of tissue which extends throughout the whole 

 length of the pod, and is no wider at any point than is the con- 

 striction \vhich occurs between the seed chambers. The outer 

 layer, on the other hand, is the part which gives the form to the 



