123 FERTILIZATION. 



observation of others. All botanists, who have investigated 

 this subject, agree that the pollen tubes enter the ovule and 

 come in contact with the sac ot' the amnios. The result pro- 

 duced by this contact, is thus given by Mr. Griffith, as quoted 

 by Prof. Lindley, in his third Edition of the introduction to 

 Botany, p. 343. "The pollen tube in first coming in contact 

 with the sac of the amnios, in the santalum album becomes 

 blended with it, without perforating the membrane. The 

 molecular matter has at this time lost its locomotivity, and 

 becomes aggregated into a grumous line, reaching from the 

 apex of the sac to its base. Then a globular vessicle, con- 

 taining mobile granules, appears at the apex of the sac, in 

 communication with the grumous molecular line. About the 

 same time, a distension of the base of the sac occurs, and a 

 central cell is formed in it ; by degrees the space intervening 

 between the latter and the apex of the sac, becomes cellular 

 and changes to asuspensor, having an embryo at that end 

 which is next the base of the sac." The above is the action 

 of the pollen tube in a single case, and although they may 

 differ in some respects, yet the important points to be noticed 

 and which are the necessary circumstances attending them, 

 2ixe first that the tubes cotne in contact with the sac of the 

 amnios ; second, that the tubes do not pe;forate the membrane ; 

 and tfw'd, that by the action of the contents of the tubes, an 

 embryo is formed within the sac. These in substance, were 

 the opinions of the first observers of the action of the pollen 

 tubes, and are still those of the English, and some continental 

 Botanists. But there are those, who present the phenomena in 

 an entirely different light, and endow the different parts Avith 

 as different functions. The German Botanists, Schleiden 

 and Endleicher, are the most prominent advocates of the fol- 

 lowing theory, which is an abridgement of Schleiden's views 

 as given by Lindley. The pollen tubes enter the ovule, and 

 pass through the intercellular passages of the nucleus, and 

 reach the embryo sac, which, being forced forward, is pressed, 

 indented, and becomes the cylindrical bag which constitutes 

 the embryo in this first stage of its development ; and which 

 consequently consists solely of a cell of parenchyma, sup- 

 ported upon the summit of the axis. This bag is therefore 

 composed of a double membrane, (except the open radicular end,) 

 viz : the indented embryo sac, and the membrane of the pollen 

 tube itself. In Taxus, and especially in Orchis, he has suc- 

 ceeded in drawing out that part of the pollen tube from the em- 

 bryo sac, which becomes the embryo, and that too, at a con. 

 siderable advanced stage. 



