1902] A MORPHOLOGICAL STUDY OF ASCLEPIADACEAE 393 



the reflexion of the epidermis where the two whorls unite, and 

 from the meristematic character of the cells composing the ring, 

 one is led to conclude that it is of toral origin. The whole 

 stamen in its older stages shows a remarkable tendency to form 

 intercellular spaces, the tissue resembling the spongy parenchyma 

 of a leaf. 



The filaments unite to form a ring about the carpels. By 

 their growth upwards against the head the anthers are pushed 

 into a lateral position {figs. g-ii). At five points, corresponding 

 to the five lines along which the filaments have united, they do 

 not fit up against the head so tightly. These are the gateways 

 to the stigma. 



At the base of the united stamens are two spaces somewhat 

 tetrahedral in form, bounded by the stamineal ring and the two 

 carpels. The general tendency towards the formation of loose 

 tissue expresses itself here in the formation of two protuber- 

 ances from the base of the stamineal ring, filling these spaces 

 {fig's. 20, 2iy They are large enough to be seen easily with the 

 naked eye and might be taken for rudimentary carpels, but their 

 late appearance and the bulging of the stamineal tissue into them 

 reveals their origin. Eichler (6) figures diagrammatically what 

 he calls disk glands in a similar situation in Vinca minor. But 

 these projections in Asclepias, while easily mistaken for glands 

 under a hand lens, do not give the dense stain obtained in other 

 glandular tissue of the flower. 



Just before the ovules appear, when the pollen has reached 

 the mother-cell stage, the filament pushes out on its dorsal side 

 a crescentic protuberance whose convex side is towards the base, 

 and in whose concavity a papilla appears {fig^ 16). The cre- 

 scentic projection is destined to become the hood, and the 

 papilla the horn. The young hood and horn are meristematic 

 at the tip. Spiral vessels appear in the one bundle of each sta- 

 men about the time the hood begins to grow. These bend, 

 forming a loop in the hood as it grows larger. When the latter 

 has reached its full development, the vessels extend seven-eighths 

 of the distance to the tip and bend sharply back upon them- 

 selves [fig, 18), The vessels in the filament must have increased 



