304 FERTILIZATION. 



horn's suffice for their passage through even the longest styles, such 

 as those of Colchicum, Mirabilis or Four-o'clock, and Cereus grandi- 

 florus. After the pollen-tubes have penetrated the stigma, the latter 

 dries up, and its tissue begins to wither or die away, as likewise 

 does the body of the pollen-grain, its whole contents being trans- 

 ferred to the pollen-tube, the lower part of which may still be in a 

 growing condition. 



577. Before the pollen-tube has reached the ovule, or more com- 

 monly even before the pollen is applied to the stigma, a cavity ap- 

 pears in the interior of the nucleus of the ovule, near its apex. 

 This probably results from the special growth of a particular cell, 

 which expands into a bladder or closed sac, at length commonly oc- 

 cupying a considerable part of the nucleus, — sometimes remaining 

 enclosed in its tissue towards its summit or orifice, sometimes dis- 

 placing the upper part of the nucleus entirely, or even projecting 

 through the micropyle. This is the sac of the amnios of Mr. Brown, 

 the embryo-sac (sac embryonaire) of the French botanists. In this 

 sac the embryo is formed. 



578. Origin of 1 lie Embryo. From the latter part of the seven- 

 teenth century, when the relative functions of the stamens and the 

 pistils, and something of the structure of the ovule, were demon- 

 strated by Malpighi, Grew, &c, until about the year 1837, it was 

 almost universally supposed that the embryo was a product of the 

 ovule, in some way incited or fertilized by the pollen. One writer, 

 viz. Samuel Morland, had indeed propounded the crude hypothesis, 

 that a pollen-grain itself, descending bodily through the style, was 

 received into the orifice of the ovule, and became the embryo. The 

 absurdity of this view was soon made evident. But how the pollen 

 acted was wholly unknown until Amici, in 1823, discovered pollen- 

 tubes, penetrating the stigma, and Brongniart, Brown, Amici himself, 

 and Schleiden, within the ensuing twelve or fourteen years, had 

 demonstrated their universality, and traced these slender tubes into 

 the ovary, and even to the nucleus of the ovule. Then commenced a 

 spirited controversy, which has only just now been brought to a close. 

 For Professor Schleiden, in the year 1837, advanced the view that the 

 extremity of the tube of the pollen, entering the nucleus of the ovule, 

 there developed into the embryo, — thus anew deriving the embryo 

 or new plant substantially from the pollen instead of the ovule. 

 This view has recently been abandoned by its indefatigable author 

 and his mo it able supporter, Schacht, having been thoroughly dis- 



