LTNNEAN SOCTETT OF LOXDON. 65 



search for it in other Orders than Orchideix>, and thus establish its 

 " prevalence " ui the cells, first of Monocotyledons and then of 

 Dicotylt dons. Pnrsuing the investigation, on examining the hairs 

 on the filaments of Tradescantia, he discovered the circulation 

 of currents of granular matter within their component cells, of 

 which currents he says tliat their course seemed often in some 

 degree " to be aftected by the nucleus, towards or from which many 

 of them occasionally tended or appeared to proceed." The 

 supreme importance of this observatioii as the first stage in the 

 history of cell-growth and multiplication, leading to undreamt 

 of conceptions of the fundamental phenomena of organic life, is 

 acknowledged by all investigators. 



The Asclepiadecs are treated of in the same masterly manner, 

 with the same completeness as the Orchidece, and with even 

 more striking results in respect of the processes of fecundation. 

 Of the latter 1 will mention only the simultaneous bursting of 

 every pollen-grain of the pollinium at the moment of its contact 

 witli the stigma, and the expulsioji from one and always the same 

 point of its surface of the pollen-tubes, collected in the form of 

 cords. In his description of this mysterious phenomenon he 

 says : — " As there are no visible conductors of this stimulus (from 

 the stigma) within the mass, it must either be supposed to be 

 propagated from one cell to another, or conveyed from the pro- 

 minent point of the edge (of the pollinium) to every other part 

 of the surface of the covering itself." In conversation with me, 

 Mr. Brown has talked of this singular phenomenon as an inscru- 

 table mystery. 



Throughout these investigations the behaviour of the pollen- 

 tube seems to have been the leading object of study, and especially 

 its descent and insertion into the foramen of the ovule. In 

 searching out this matter, his patience seems to have been equalled 

 only by his extreme caution, for even after having seen the 

 connection in some plants, and failed to find any insuperable 

 objections to its occurring in others, he concludes with the 

 following remark : — " Though the descent of tubes derived from 

 the pollen into the cavity of the ovarium, and their insertion into 

 that point of the ovulum where the radicle of the future embryo is 

 seated, has been absolutely ascertained in several species of Or- 

 cJiidecB and in one of Asclepladece, and probably will be found iu 

 the whole of these extensive families, yet it does not follow 

 that the descent and insertion of the tubes should be expected to 

 extend to all phanerogamous plants ; for among these some 

 structures of the female organ exist which hardly admit of this 

 economy"*. 



Amongst other curious observations in these memoirs is that of 



* It would be interesting to know to what planls Brown here alludes — pos- 

 sibly to such Eiiphorbiaccce as have the ovule cajiped by a caruncle or obturator. 

 He cannot allude to arillate ovules, for he elsewhere observes that the aril does 

 not cover the foramen until after impregnation. 



LINN. SOU. PKOCEEDINUS. — SESSION 1887-88. f 



