400 Cytological Features of Fertilisation, fyc., in Pinus silvestris. 



" On the Cytological Features of Fertilisation and related 

 Phenomena in Pinus silvestris^ L." By VERNON H. 

 BLACKMAN, B.A., F.L.S., Hutchinson Student, St. John's 

 College, Cambridge, and Assistant, Department of Botany, 

 British Museum. Communicated by FRANCIS DARWIN, 

 F.R.S. Received May 3, Read May 26, 1898. 



(Abstract.) 



This paper gives a fairly complete account of the minute Cytological 

 details of the act of fertilisation and of the processes surrounding it, 

 from the formation of the ventral canal cell up to the period of cell- 

 wall formation at the base of the egg. 



As the oosphere nucleus, after separation of the nucleus of the 

 ventral canal cell, moves rapidly back towards the centre of the egg, 

 it increases greatly in size, as described by Strasburger. This 

 increase in size is shown to be due to the appearance in the nucleus 

 of a peculiar metaplasmic substance, which fills up the nucleus, and, 

 owing to its attraction for stains, ultimately obscures the chromatin. 

 The mature female nucleus, which is sometimes large enough to be 

 visible to the naked eye, exhibits merely an uniformly staining reticu- 

 lum composed chiefly of metaplasmic substance, with one or more 

 nucleoli. 



By the rupture of the closing membrane of the well-marked pit 

 at the apex of the pollen tube, almost the whole of the contents of 

 the lower part of the tube pass over into the oosphere. At this 

 stage all the four nuclei, together with a considerable number of 

 starch grains from the pollen tube, are to be seen lying in the cyto- 

 plasm of the egg. Cytoplasm from the pollen tube must also 

 necessarily pass over, and with it the plastid-lik-e structures to be 

 seen earlier in the cytoplasm of the generative cells. 



The behaviour of the four nuclei in the egg was carefully followed ; 

 the stalk cell nucleus, the pollen tube nucleus, and one generative 

 nucleus remain at the apex of the egg, near the point of entry, and 

 ultimately become disorganised. The other generative nucleus, 

 which possesses distinct nucleoli, as does also its sister nucleus, 

 advances very rapidly towards the female nucleus, increasing some- 

 what in size and in mass of staining material on its way. After 

 coming in contact with the much larger female nucleus it gradually 

 penetrates the substance of the latter until it is almost completely 

 enclosed within it, but breaking down of the nuclear walls, that is, 

 actual fusion, is for some time delayed. After fusion has taken 

 place, but while the outlines of the two nuclei are still distinct, 

 the chromosomes can be distinguished as two separate groups derived 



