726 Mr. Brown on the Organs and Mode of 



the obstacles opposed to them ; and such tubes very seldom 

 enter the style, but along with others hang down externally be- 

 low the joint. This introduction of part of the tubes into the 

 apex of the style is soon followed by a manifest enlargement of 

 the ovarium, and of the style itself, which, in Asclepias purpu- 

 rasce7is, then exhibits a discoloured blackish line, visible even 

 on the surface of its inner side. On opening the cavity or body 

 of the style in this stage, a fasciculus of tubes was constantly 

 seen passing down the centre, which was originally pulpy, and 

 the walls of the cavity formed by the passage of these tubes 

 was always found indurated and blackened, having every ap- 

 pearance of being absolutely killed. 



I have never been able hitherto to follow these tubes further 

 than the commencement of the placenta, where they really ap- 

 pear to terminate*. I have not at least j'^et succeeded in tracing 

 any of them either on the surface or in the substance of the pla- 

 centa, though with this object I have examined it not only in 

 its first degree of enlargement, but also in some of its more ad- 

 vanced stages. 



The same series of appearances, with very slight modifications 

 only, were observed in all the species of Asclepias (not indeed 

 more than seven in number) which I had opportunities of ex- 

 amining during the summer. For in those species in which the 

 pollen mass was not found transferred from its original position 

 to the fissure, and in contact with the base of the style, no doubt 

 by means of insects, it was not difficult to place it there ; and in 

 doing so I never failed to obtain the same results. 



I now turned my attention to the base of the stigma, expecting 

 to find there such a modification of surface as might serve to 

 account for the rupture and production of the tubes in the mass 

 brought in contact with it. I have, however, in no case been 



• Tab. 34, fig. 10, 8c 1 1 ; and Tab. 35. fig. f,, & 6. 



able 



