STRASBURGER : FERTILISATION OF PHANEROGAMS. 



most serviceable, though Monotropa, Torem'a, and species of Gloxinia 

 and Lilium have also been employed with advantage. Various 

 methods of treatment, details of which are always given, were 

 adopted in deaUng with the selected material, and the views now 

 pubHshed are based upon the results of the whole series of investi- 

 gations. Before summarising these, it will facilitate our task, and 

 conduce to greater clearness, if we describe very briefly the organisa- 

 tion of the embryo-sac, in which the process of fertilisation actually 

 occurs. 



The embryo-sac of an Angiosperm is usually an elongated cell 

 lying longitudinally in the nucellus of the ovule. The end which is 

 turned towards the micropyle may project into that cavity, or it may 

 be separated from it by a single layer of cells. The chief structures 

 contained within it are (i) a pair of nucleated protoplasmic bodies 

 placed at the micropylar end, termed the synergidce ; (ii) two or three 

 similar bodies at the opposite end called the antipodal cells ; and 

 (iii) the egg-cell or oosphere, a nucleated protoplasmic mass, usually 

 situated just below the synergidce. It need hardly be said that the 

 egg-cell is the most important structure contained within the embryo- 

 sac. Its nucleus plays a leading part in the act of fertilisation, and 

 out of the cell as a whole, the embryo is subsequently developed. 



When the ovule is ready for fertilisation the synergid^ are often 

 streaked longitudinally, while each develops for itself a small re- 

 fractive cap at its micropylar end. Over these caps, the delicate wall 

 of the embryo-sac is resorbed, so that towards the micropyle, the 

 cavity of the sac is open. 



By this time the pollen-tube has traversed the style and entered 

 the ovary, where, stimulated by a substance encreted by the syner- 

 gidse, its direction of growth is so changed that it advances along the 

 funiculus and enters the micropyle. Its tip having reached the caps 

 of the synergidae ceases growing, but the protoplasm passes through 

 the membrane at the tip and travels between these structures towards 

 the egg-cell. Strasburger previously assumed that the plasma of the 

 pollen-tube was absorbed by one or both of the synergidse, but he 

 now admits that this was an error, and explains otherwise the appear- 

 ances which led to it. Indeed, at the moment when the pollen-tube 

 reaches the apex of the ernbryo-sac, one or both the synergidae 

 become disorganised, one of their functions, viz., that of indicating 

 the way to the egg, being now completed. The protoplasm of the 

 pollen-tube, moving forwards towards the egg, carries with it the two 

 generative cell-7iuclei, which now become the male or sperm nuclei 

 that previous observers have seen in copulation with the nucleus of 

 the egg. These nuclei, being of equal value, each may effect fertilisa- 



:\Iarch 1885. 



