IN PLANTS. 61 



embryo-sac before it becomes detached from the rest of the tube, and 

 constitutes the first rudiment of the future plant, has been opposed by 

 Professor Amici,* the celebrated Italian botanist, to whom we owe 

 the discovery of the emission of tubes by the pollen grains. From 

 observations made on the Cucurbita Pepo, Amici appears to have clearly 

 ascertained that, although the extremity of the pollen-tube enters the 

 nucleus of the ovule to a certain depth, yet, it never penetrates the 

 embryonic sac ; and he thinks it probable that the contents of the sac are 

 fecundated by an absorption through its membranous wall of the im- 

 pregnating fluid of the pollen-tube, which is situated in the immediate 

 neighbourhood of the sac, or even on its external surface. As other reasons 

 against the supposition that the extremity of the pollen-tube itself becomes 

 the embryonic vesicle from which the embryo is formed, he observes, that 

 this vesicle exists previous to the fecundation of the ovule, and that, after 

 fecundation, its development commences at the opposite point to that at 

 which the pollen-tube exercises its influence. Moreover, the true embryo 

 of the plant may be distinctly recognised before it has acquired a diameter 

 equal to that of the pollen-tube from which it has been supposed directly 

 to spring. His investigations, likewise, into the mode of fecundation 

 as pursued in the Orchidacese, have shewn him that in these plants also, the 

 extremity of the pollen-tube is not converted into the embryo. 



M. Tulasnef, on the other hand, from the examination of three species of 

 Veronica and other plants, expresses himself as favourable to Schleiden's 

 opinion. He states, that he has many times observed the pollen-tube to 

 penetrate the embryo-sac, and this apparently by perforation. At no 

 period has he been able to detect any thing which could be called an em- 

 bryonic vesicle. He observes, that when the embryo-sac commences to 

 enlarge, the plastic matter which it contains becomes developed into cells 

 from the circumference towards the centre. During the early part of this 

 cell-forming process, the pollen-tube within the embryo-sac remains ap- 

 parently unaltered, and filled with grumous-looking material. Shortly, 

 however, this material breaks up, and the tube which contains it becomes 

 divided by a number of transverse septa into so many cells, which divide 

 and subdivide : and then, in the midst of the resulting mass, the embryo 

 appears. An opinion rather favourable to the penetration of the pollen-tube 

 into the embryo-sac in the ovulum of Avicennia, has also been expressed 

 by the late Mr. Griffith.! 



* An. des Sc. Nat. Avril, 1847. t Comptes Rendus, 14 Juin, 1847, p. 1060. 



| Transactions of the Linnaean Society, vol. xx. 1846, p. 1 6. 



