536 ON THE ORGANS AND MODE OF FECUNDATION 



Fig. 2. A grain of pollen, of the same species, with a portion of its tube ; 

 the unusual form probably caused by the pressure of other grains and their 

 tubes. 



Fig. 3. A grain of pollen of Asclepias purpiirascens containing numerous 

 minute granules and two larger drops or globules of an oily fluid. 



Figs. 4, 5, & 6. Various combinations of pollen masses of Asclepias puqmr- 

 ascens. In these it is supposed that the insect having removed and applied to 

 the stigma some of the masses, has extracted, by means of the arms still 

 adhering to it, other masses with their glands and arms. 



A combination of the same kind, different from and more remarkable than 

 any of these, but perhaps not very accurately represented, is given, in his 

 Microscop. E/itdeck., tab. 36, fig. 8, by Gleichen, who appears (op. cit. p. 81) to 

 have also met with other combinations, without suspecting in any case the 

 real cause of such apparently anomalous structures. 



Fig. 7. A flower bud of Asclepias curassavica in the earliest stage in which 

 I was able to distinguish its parts ; the unopened corolla in its place with one 

 of the sepala, the other four being exhibited separately : — highly magnified. 



73S] Y\g. 8. The Corolla of fig. 7, opened and in part removed, to show the state 

 of the contained organs ; the figure exhibiting two petals hardly cohering at 

 base ; within these, two distinct petal-like bodies, alternating with them, and 

 which are the antherae ; and two other smaller bodies, which are the pistilla as 

 yet unconnected. 



Fig. 9. An Anthera taken from fig. 8, and more highly magnified, to show 

 that in this early stage it is entirely petal-like, there being no indication of the 

 two cells, of which the first appearance in a somewhat more advanced stage is 

 given at Fig. 10. 



Fig. 11. A Petal of fig. 8, more highly magnified. 



Fig. 12. The Pistilla of fig. 8, as yet distinct, scarcely at all angular, and 

 with no manifest cavities ; so that these two bodies may be regarded as chiefly 

 or entirely the component parts of the stigma. 



Fig. 13. Two Grains of pollen taken from the pollen mass of the expanded 

 flower of Asclejms curassavica. 



