PHANEROGAMIA : FLOWERS. 413 



on fecundation to the Linnaean Society, in which Schleiden's view of the 

 origin of the embryo from the pollen-tube is confirmed. The observa- 

 tions in Santalum are the most sure. In Loranthm the pollen-tubes 

 undoubtedly traverse the whole embryo-sac." 



After this exposition, I must now regard the formation of the embryo 

 from the pollen-tube as completely established, and observations dis- 

 agreeing with this can hereafter only be of value if they at once com- 

 pletely explain the cause how an error, of course not absolutely impossible, 

 could conceivably have arisen in the minds of so various, truth-searching, 

 and, with respect to Meyen in particular, certainly unprejudiced ob- 

 servers. But if science is actually to advance, all boldly-expressed 

 fancies, based on a few imperfect observations, in total ignorance of 

 what has been done before, must be wholly excluded. This especially 

 applies to the trifling, though very pretentiously delivered, new researches 

 of Amici.* It is very sad, that in a whole association of naturalists there 

 was not a single one who had the most distant idea of the imperfection 

 of this essay, or, at all events, expressed it. See my observations on that 

 Essay in the " Flora. "f 



With regard to particular points in the processes described, the fol- 

 lowing questions may yet be raised. In the first place, the mutual 

 behaviour of the embryo-sac and the pollen-tube is by no means perfectly 

 cleared up yet by observation. It remains undecided, in certain cases, 

 whether the membrane of the embryo-sac, which in this way becomes 

 pushed inward and forms an investment over the apex of the pollen- 

 tube, does not subsequently perhaps become dissolved and absorbed, so 

 that the pollen-tube actually penetrates directly into the cavity of the 

 embryo-sac, which is certainly very probable in those plants in which the 

 pollen-tube goes down a disproportionately long way into the embryo- 

 sac, as in many species of Veronica, in the Santalacece, in Marty nia 

 diandra, where it descends almost to the chalaza ; in some, e. g. in Phor- 

 mium tenax, a distinct investment of the pollen-tube clearly remains for 

 a long time. This much is certain, that in all cases where I was certain 

 that the object was still in its natural position, especially where I suc- 

 ceeded in laying bare the apex of the embryo-sac and pollen-tube in the 

 section, without removing them from their proper places in the seed-bud, 

 I saw the membrane of the embryo-sac curve over at the apex, and run 

 inward on the pollen-tube. But it is quite possible that the embryo-sac, 

 originally somewhat pressed inward by the entering pollen-tube, being 

 of course very thin and delicate at this time, sometimes even merely of a 

 gelatinous consistence, may become dissolved gradually from the apex of 

 the pollen-tube, so that the latter shall actually break through it. Such 

 a gradual solution must, at the same time, obliterate every sharply- 

 defined border, which certainly is never seen. It may be, however, that 

 the embryo-sac is only expanded out, so as to become very thin. The 

 possible modifications do not appear to me to be important here, since 

 by the subsequent construction the embryonal vesicle comes also to lie in 

 the cavity of the embryo-sac, and of course, after cell-formation begins, 

 not merely any possible coating of membrane of the embryo-sac, but also 

 the pollen-tube itself, disappears from observation (becomes absorbed). 

 With regard to that, I may remark that the transformation of the ger- 

 minal vesicle into the embryonal globule by the formation of cells within 



* Flora, 1844 and 1845, p. 193. 



t Flora, 1845, pp. 787. and 593. ot seq. 



