136 K. Miy ake, Contribut. to the Fertiliz. and Embryogeny of Abies balsamea. 



those of the egg-nucleus (Figs. 14 — 17). Investigators of Pinus 

 found that the ventral canal-cell shows signs of disintegration veiy 

 early in its history, sometimes even before the formation of the 

 nuclear membrane (Blackman ' 98, Chamberlain ' 99, Miss Ferguson 

 ' Ol). I found a sirailar case in Picea. In Tsuga, however, accord- 

 ing to Murrill (' 00) the ventral canal - cell seems to keep its normal 

 appearance much longer. Ile states that, — „When division is 

 completed, its nucleus is equal in size and similar m structure to the 

 nucleus of the ^g^, and for some time shows the same stages of 

 development." It is interestüig to note how the position of the 

 nucleus of the central cell before division, affects the size and per- 

 sistency of the ventral canal-cell, as can be seen by comparing 

 Pinus and Picea on the one band with Ahies and Tsuga on the 

 other. The natui^e of the ventral canal-cell may, therefore, be pre- 

 dicted before its formation by merely observing the position of the 

 nucleus of the central cell. 



The nucleus of the ventral canal -ceU enlarges several times 

 after its formation, and fills a larger part of the cell (Figs. 13—17). 

 When the nucleus reaches its füll size, signs of disintegration appear. 

 The ventral canal-cell usually persists until the time of fertiüzation, 

 and after the entrance of the poUen-tube contents, its nucleus is 

 often seen near the apex of the Qgg, being probably pushed in by 

 the inrush of the tube- contents. The nucleus at this time, in a 

 section treated with triple stains, has a pui^ple-stained reticulum and 

 a red-stained nucleolus (Figs 31, 34, 41). The ceU-wall separating 

 the ventral canal-cell from the egg is broken down and can no longer 

 be seen about this time, although part of it is sometimes found at 

 the apex of the Qgg (Fig. 35). 



When the division of the central cell is completed, the lower 

 of the two daughter nuclei namely the egg-nucleus, begins to in- 

 crease rapidly in size and at the same time to move down towards 

 the centre of the %gg. This takes place even before the complete 

 disappearance of the spindle-fibres. As the nucleus moves down 

 towards the centre of the %gg, it continues to enlarge until the 

 centre is reached (Figs. 3 — 5, 14—18). 



When the egg-nucleus reaches maturity it attaiiis a huge size, 

 its average diameters being 140 to 160 /* by 100 to 120^. (Fig. 18). 

 Its outline is usually oval or elbptical and rarely subspherical. A 

 nucleus wliich was found to approach a spherical form is sketched 

 in Fig. 20; one which is somewhat pear-shaped was foimd in a few 

 cases (Figs. 21, 23). The egg-nucleus usuaUy contains a more or 

 less interrupted reticulum which appears somewhat granulär and 

 takes a pm^ple stain in the triple method. It usually has one large 

 nucleolus, and several smaller ones. 



Not infrequently the egg-nucleus has a diflferent structure from 

 that which has been mentioned above. The ground mass of the 

 nucleus takes a very little stain, presents a homogeneous appearance; 

 and numerous nucleolus-üke bodies together with the irregulär frag- 

 ments of chromatic substance are scattered throughout the nuclear 

 cavity (Figs. 23 — 25). In a few cases the ground substance of the 

 nucleus presented a faintly staining rather flne reticulum, with 

 numerous nucleolus-like bodies of various sizes scattered throughout 



