Linncean Society. 441 



from the cells, and apply tliem to the apex of the stigma, which, being 

 a secreting part, is calculated to act on the oily matter exuding from 

 the surface of the pollen mass. 



In 1829 Ehrenberg describes the grains of pollen as contained in 

 the proper membrane of the mass, which bursts in a regular manner, 

 and as having each a tube, which tubes collectively are directed 

 towards the point of dehiscence. He does not say how they communi- 

 cate with the stigma, and supposes that they form an integrant part 

 of the grain, without being produced by the action of an external sti- 

 mulus. 



In July last Mr. Brown resumed his investigations into the struc- 

 ture and functions of the organs of this family. He verifies observa- 

 tions made by Mr. Bauer so early as 1 805, that the masses are cellu- 

 lar, each cell containing a single grain. These cells he considers as 

 the outer membranes of the grains of which the inner membranes are 

 the grains described by Treviranus without tubes, and by Ehrenberg 

 after their production. 



He found that the agency of insects was necessary to efl'ect fecun- 

 dation ; that the pollen masses were actually removed from the cell 

 of the anthera, and immersed in the fissures formed by the projecting 

 alae of the antherte, the descending process of the stigma near its 

 flexure being broken, so that the mass was entirely separated from 

 the gland. The pollen mass was so placed in the fissure, that its 

 inner or convex edge was closely pressed to that point where the tube 

 of the united filaments is joined to the base of the corresponding an- 

 gle of the stigma. On separating them, a white cord, consisting of 

 slender tubes, was observed issuing from the gibbous part of the edge 

 which had burst. On opening the mass, these tubes were found to 

 proceed each from a grain of pollen, all directed towards the aperture. 

 They were like those described in Orchidece. The cord had opened 

 a passage for itself through the membrane, or, rather, had separated 

 the upper edge of this membrane from the base of the stigma, to 

 which it was before united. It then passed along the surface of the 

 base of the stigma until it arrived at its articulation with the two 

 styles ; then inclined towards the inner side of the apex, which is in 

 some degree exposed. On opening the cavity of the style, the cord 

 was seen passing down the centre to the commencement of the pla- 

 centa, where it appears to terminate. 



These appearances, which were the result of the application of the 

 pollen to the base of the stigma by insects, were equally obtained by 

 Mr. Brown's removal and application of the mass. He found that the 

 convex edge of the mass must be the part applied, though he could 

 detect nothing peculiar in its structure or appearance. At present 

 he has not had sufficient opportunities to di.scover how impregnation 

 is eft'ected in those plants of this family which have erect pollen 

 masses ; for though he has succeeded in producing the tubes in Hoya 

 carnosa, he could not get them to communicate with the stigma, nor 

 can he conjecture how this is to be etlectcd. 



N. S. Vol. 10. No. 60. Dec. 1831. 3 L astro- 



