1899.] NATURAL SCIENCES OF PHILADELPHIA. 105 



We may uow conclude that there is uo special mystery to be 

 solved in the flower of Asdepias. The structure is very simple. 

 The parts, as Ave conceive them primarily to be, are all there, 

 and in their regular places. The tendency to arrestation and union 

 accounts for what seems strange. 



With the elucidation of the real structure of the flower, other 

 mysteries will dissolve. No one has been able to explain the 

 manner in which the flower is pollinized. The accepted hypothesis 

 is the chance transference of a pollen mass to the disc by means of 

 an insect's foot. The abundance and regularity of seed vessels 

 on many species should at once discredit such a notion. Eegularity 

 does not follow accident. In almost every umbel in Asdepias 

 incarnata, there are regularly one or two fertile flowers, and this is 

 true of other species. As the anther cells rupture, the pollen mass 

 is in close contact with what I have shown is the real stigmatic 

 surface. The flower is an absolute self-fertilizer, and can receive 

 no aid from the visits of insects. 



The failure of so many flowers to mature fruit is a matter of 

 nutrition. It has already been seen how easily the axillary bud is 

 induced to displace the leader, by the diversion of nutrition in that 

 direction. There are always two ovaries and corresponding styles 

 in each flower of Asdepias. If we open a fertile flower in an early 

 stage of its advance to a fertile condition, we may note that the 

 stronger one has simply starved the other. 



There are other matters in connection with the life-history of 

 Asdepias well worthy of iavestigation. In Asdepias tuberosa, as 

 in some other species, the petals reflex hurriedly when opening, but 

 close in again when near maturity. The flowers that become fer- 

 tilized coil as if they were tendrils, and indeed seem to prefer to 

 twine around some object. One might almost expect to find some 

 climbing species in the genus. It has been said that explanations 

 of this character to be acceptable should be able to account for all 

 phenomena of a similar character. In this case, what about the 

 stigmas and general features of Apocynaceie ? Surely the staminal 

 verticil has no relation to the disc-like character of the stigma in 

 some members of the order, Vinca, for instance. But we do not 

 know how far the consolidation of parts has gone. In a double- 

 flowered oleander we note numberless petal-like organs that must 

 have had a separate starting-point, and what appears as a single 



