Yellow and Orange 



branching, spreading plant, that measures only a foot or two 

 high, appears to produce nothing but pods. These leaves re- 

 spond slowly to vibration, just as the sensitive pea's do. In spite 

 of their names, neither produces the butterfly-shaped (papiliona- 

 ceous) blossom of true peas. The partridge pea bears from two 

 to four showy flowers together, each measuring an inch or more 

 across, on a slender pedicel from the axils. It fully expands only 

 four of its five bright yellow petals ; they are somewhat unequal 

 in size, the upper ones, with touches of red at the base, as path- 

 finders, not, however, as nectar-guides, since no sweets are se- 

 creted here. Curiously enough, both right and left hand flowers 

 are found upon the same plant ; that is to say, the sickle-shaped 

 pistil turns either to the right or the left. One lateral petal, in- 

 stead of being flexible and spread like the rest, stands so stiffly 

 erect and incurved that it commonly breaks on being bent back. 

 Why ? The pistil, it will be noticed, points away from the ten 

 long black anthers. Obviously, then, the flower cannot fertilize it- 

 self. Its benefactors are bumblebee females and workers out after 

 pollen. Cup-shaped nectaries ("extra nuptial") are situated 

 on the upper side and near the base of the leaf stalks on these 

 cassia plants, where they can have no direct influence on the 

 fertilization of the blossoms. Apparently, they are free lunch- 

 counters, kept open out of pure charity. Landing upon the 

 long black anthers with pores in their tips to let out the pollen, 

 the bumblebees "seize them between their mandibles," says 

 Professor Robertson, "and stroke them downward with a sort 

 of milking motion. The pollen . . . falls either directly 

 upon the bee or upon the erect lateral petal which is pressed close 

 against the bee's side. In this way the side of the bee which is 

 next to the incurved petal receives the most pollen. ... A 

 bee visiting a left-hand flower receives pollen upon the right side, 

 and then flying to a right-hand flower, strikes the same side 

 against the stigma," When we find circular holes in these petals 

 we may know the leaf-cutter or upholsterer bee {Megachile brevis) 

 has been at work collecting roofs for her nurseries (see page 6i). 

 The partridge pea, which has a more westerly range than the 

 sensitive pea's, extends it southward even to Bolivia. Game 

 birds, migrants and rovers, which feed upon the seeds, have of 

 course helped in their wider distribution. The plant blooms from 

 July to September. 



Wild or American Senna 



{Cassia Marylandica) Senna family 



Flowers — Yellow, about ^ in. broad, numerous, in short axillary 

 clusters on the upper part of plant. Calyx of 5 oblong lobes; 



308 



