558 ORGANOLOGY. 



and the action of humidity, until the cell itself is in a state fit to 

 assimilate foreign matters. 



b. Phanerogamia. 



223. With regard to the anthers, the parent-cells form the 

 pollen, and the external, and frequently so richly and curiously- 

 formed membrane seems to perform no other function than that of 

 the spore-case alluded to at the conclusion of our last paragraph. 

 The formations, secreting surfaces, or organs that secrete sweet 

 juice, the true nectar, have no imaginable organic connexion with 

 the function of reproduction; but they appear to attract the insects, 

 which latter so frequently assist in the transfer of the pollen to the 

 stigma. 



The seed-bud (ovule) is intended for the reception of the pollen- 

 tube. It is protected by the germen in the same manner as the 

 terminal shoot is by the external leaves of the bud, and at the same 

 time it conveys to it the pollen-tube. 



The most important part of the seed-bud is the embryo-sac, 

 because the embryo (with the exception of the Rhizocarpece) is 

 developed in it. We are as yet entirely ignorant of the influence 

 which this sac exercises on the embryo. 



It is certain that granules of pollen produce genuine tubes in other spots 

 besides the stigma ; it is also certain that many pollen-tubes descend 

 through the stigma and style into the cavity of the germen, without 

 being converted into embryos, because they have not penetrated the seed- 

 bud. But it is likewise as certain, that the tubes in the Rhizocarpece do 

 not come into immediate contact with the embryo- sacs, being constantly 

 separated from them by a thin layer of cells. An observation of my own, 

 referred to on a former occasion *, is also highly remarkable, viz., that 

 two pollen-tubes entered into the seed-bud of an Orchid, one of which, 

 penetrating through its internal opening, reached the embryo-sac, and 

 pressing upon this was converted in the usual way into an embryo, 

 whilst the other penetrated between the external and internal covering 

 of the seed-bud, and was developed into the rudiment of an embryo (a 

 kind of graviditas extrauterina) (see Plate VI., fig. 1.). It appears, 

 therefore, that the influence of the embryo-sac may extend to some dis- 

 tance, but it is entirely unknown to us what kind of influence; and it is 

 the more difficult to be discovered, as the most important elements in the 

 enquiry, viz., an accurate chemical investigation of the contents of the 

 pollen-tube and of the embryo-sac, are not yet forthcoming, and are not 

 likely to be so for a long time to come. I may here remind my readers 

 of Caspar Fr. Wolff's expression, " Nutrimentum magnum in minima 

 mole." As to analogies between the production of plants and the pro- 

 creation of the higher animals, it can merely afford employment for the 

 wit of those who have nothing better to do, since the act itself, and the 

 part which the different materials play in it, are as yet entirely unknown 

 to us, even with regard to the higher animals. 



* Acta. Acad. C. L. C. N. E. vol. xix. pt. i. p. 46, in Orchis latifolia. 



