THE SEED PRODUCTION OF PIN US SYLVESTRIS. 21 



which fills the space recently occupied by the cells I have 

 ventured to regard as tapetai, fragments of these latter are 

 numerous ; there are still two or three layers of the tabular- 

 cells bounding the cavity ; they are, however, rapidly 

 disappearing, the last few days of their existence being 

 characterised by the phenomena of unequal amitotic 

 division, and polynucleated cells. 



The cells immediately surrounding the young arche- 

 gonia, and which constitute the four layers, are known as 

 jacket cells ; they form an almost complete envelope or 

 jacket around each archegonium. They persist and 

 function until the pro-embryos are laid down. 



By the last week of May the central cells of the 

 archegonia have grown considerably, being now about 250 

 microns in length and 100 microns in diameter ; the nuclei 

 are about 32 microns in diameter, and are at the apex of 

 the cell immediately beneath a single row of four neck 

 cells. In a few days — first week of June — the central cells 

 are nearly -1-00 microns long ; the nuclei have corre- 

 spondingly increased in size ; the single layer of neck 

 cells have divided, there being now two layers of four cells 

 each ; the endosperm ot the gametophyte has extended at 

 the apical end, leaving the neck cells at the base of a short 

 funnel-shaped tube. Growth proceeds rapidly, and about 

 the end of the third week of June the nucleus of the 

 central cell (it will be well now to deal with the individual) 

 is ripe for division ; it is now about 50 microns in 

 diameter. It is still situate at the apex of the cell, the 

 cytoplasm of which is vacuolated, usually one large 

 central vacuole surrounded by a number of smaller ones 

 (fig. 6). The ripe nucleus now divides, producing at the 

 apical end what is known as the ventral canal cell, and at 

 the other the egg cell. The former is a very small cell, 

 which together with its nucleus at once commences to 



