Origin and Development of the Vegetable Embryo. 61 



From the preceding statements we gather the following gene- 

 ral statement of the process of impregnation. 



At the period of the opening of the flower the embryo-sac ex- 

 ists, and at its upper (micropyle) end one or more cells (germinal 

 vesicles) are produced from cytoblasts. The pollen-tube makes 

 its way down the style into the ovary, and finally through the 

 foramina of the coats of the ovule, and comes in contact with the 

 embryo-sac ; here it either applies itself immediately upon the 

 apex or proceeds a little way further, so as to lie rather on the 

 side of the apex of the embryo-sac. Hereupon (and probably as 

 a result of the imbibition of the fluid of the pollen-tube through 

 the membranes) the cell, or one of them if there are more, lying 

 in the embryo-sac, begins to develope, and in course of time 

 produces the embryo. 



We may glance at the evidence to be obtained from the accounts 

 given by authors who deduce conclusions different from the above. 

 Meyen* believed that the phsenomena presented themselves with 

 two modifications ; the first where the embryo-sac evidently exists 

 before impregnation, and the second where, as he believed, this 

 is wanting at that period. The latter modification, where he said 

 that the germinal vesicle is produced by the end of the pollen- 

 tube, cannot be brought into relation with the theory under exa- 

 mination, but the latter presents some points of resemblance. In 

 this case he stated that the pollen-tube comes in contact with 

 the embryo-sac and becomes united with it, and then the ger- 

 minal vesicle makes its appearance in the embryo-sac. But in 

 one instance which he figured, namely in Mesembryanthemum glo- 

 meratumf, he confessed that the absorption of the membranes 

 separating the cavities of the pollen-tube and embryo-sac was an 

 assumption, and the figure in question exactly resembles Miiller's 

 representation of the phsenomenon, the pollen-tube lying rather to 

 the side of the summit of the embryo-sac. If we could believe 

 that he was mistaken in supposing that an actual union of the 

 embryo-sac and pollen-tube took place (and in such investiga- 

 tions graver errors are easily fallen into), the only point of differ- 

 ence would be with regard to the period when the germinal vesicle 

 is first produced. 



In reference to Schleiden's opinions, the view which he first 

 promulgated was that the pollen-tube pushed the summit of the 

 embryo-sac before it and became invested by it; but in the last 

 edition of his ' Grundziige J', he admits the possibility in certain 

 cases of the actual entrance of the pollen-tube into the embryo- 



* Pflanzen-physiologie, vol. iii. 



f Op. cit. vol. iii. pi. xiii. figs. 46, 47. 



J Grundz. des Wiss. Botanik, 2nd edit. ii. 366. 



