46 THIRD REPORT — 1833. 



pollen, have been removed; the important demonstration by 

 Dr. Brown of the universal presence of a passage through the 

 integuments of the ovulum at the point of the nucleus has been 

 extended and confirmed by M. Mirbel in a paper of the high- 

 est interest * ; the fact that it is at the point of the nucleus (where 

 this passage exists,) that the nascent embryo makes it appear- 

 ance, is now undisputed; the passage of the contents of the 

 pollen down the pollen-tubes, and the curious discovery of a 

 power of motion in the granules that are thus emitted, are also 

 recognised : it now only remains to be proved that the pollen- 

 tubes come in contact with the nucleus, and the whole secret of 

 fertilization is revealed. A few remarkable conti'ibutions to 

 this part of the subject have lately been made. 



Some plants have the passage or foramen in their ovulum so 

 remote from any part through which the pollen-tubes can be 

 supposed to convey their influence, as to have thrown consider- 

 able difficulty in the way of the supposition that actual contact 

 between the point of the nucleus and the fertilizing tissue is 

 indispensable. 



The manner in which, notwithstanding the apparent difficulty 

 of such contact taking place, this happens in Statice Armeria, 

 was long since made out by Dr. Brown, in whose possession I 

 several years ago saw drawings illustrating this phaenomenon ; 

 it has since been explained by M. Mirbel. Another case, pre- 

 senting similar apparent difficulties, occurs in HeUantheminn. 

 In plants of that genus the foramen is at that end of the ovulum 

 which is most remote from the hilum ; and although the ovula 

 themselves are elevated upon cords much longer than are usually 

 met with, yet there are no obvious means of tbeir coming in con- 

 tact with any part through which the matter projected into the 

 pollen-tubes can be supposed to descend. It has, however, 

 been ascertained by M. Adolphe Brongniartf, that at the time 

 when the stigma is covered with pollen, and fertilization has 

 taken effect, there is a bundle of threads, originating from the 

 base of the style, which hang down in the cavity of the ovarium, 

 and, floating there, are abundantly sufficient to convey the in- 

 fluence of the pollen to the points of the nuclei. So again in 

 Asclepiadecc. In this tribe, from the peculiar conformation of 

 the parts, and from the grains of pollen being all shut up in a 

 sort of bag, out of which there seemed to be no escape, it was 

 supposed that this tribe must at least form an exception to the 

 general rule. But before the month of November 1828 ;]:, the 



• Nouvelles Reeherches stir la Sfructurc dc VGvule Vegetal et stir ses Deve- 

 loppements. Also Additions aiix 'Nouvelles Reeherches,' Sfc. 



f Annales des Sciences, vol. xxiv. p. 123. % Linneea, vol. iv. p. 94. 



I 



