134 MORPHOLOGY OF GYMNOSPERMS 



cell. The central cell is all that remains of the " axial row " of bryo- 

 phytes and pteridophytes, true neck caiial cells having been eliminated 

 from the history of the archegonium. The primary neck cell divides 

 almost immediately, forming the two neck cells which are character- 

 istic of the whole group. After remaining for about three months 

 with little change, the neck cells grow rapidly and project prominently 

 above the general level of the surrounding tissue (figs. 135-138). 



For some time the central cell increases in size much faster than 

 in cytoplasmic content, so that a large vacuole presses the scanty 

 cytoplasm into a thin layer against the cell wall. As the central cell 

 approaches full size, its cytoplasmic content increases and it receives 

 various food substances from the surrounding tissue. This accumu- 

 lation of food substances by the central cell may be spoken of as the 

 nutrition of the egg, although in a strict sense the term egg cannot 

 be used before the mitosis which gives rise to the egg nucleus and the 

 ventral canal nucleus. During the enlargement of the central cell 

 its wall becomes greatly thickened and chemically modified, contain- 

 ing besides the original cellulose both pectin and amyloid substances. 

 The wall also becomes conspicuously pitted, and this thick pitted 

 wall is called the egg membrane. Through the pits in this membrane 

 food materials from the surrounding tissue enter the central cell, 

 although during its earlier developmental stages it receives material 

 by the ordinary methods of transferring substances from one cell to 

 another. Goroschankin (12) described pits with fine strands of 

 protoplasm connecting the jacket cells and the egg, and a year later 

 Treub (13) saw the pits in Cycas circinalis. In his work upon 

 Cycas revoluta Ikeno (27) investigated this subject and found that 

 large quantities of food material pass through the pits into the central 

 cell. He hkens this process to the passage of food materials from 

 the follicle cells into the eggs in many animals. In the Abietineae 

 Aknoldi (28) describes even the passage of entire nuclei through 

 the pits. Miss Isabel Smith (41) investigated the egg membrane 

 of Zamia floridana and found that the cytoplasm of the egg protrudes 

 through the pits into the jacket cells and forms processes which she 

 called haustoria, and showed that the structures described as nuclei 

 by Aenoldi might have been tangential sections of the enlarged ends 

 of haustoria. Stopes and Fujn (50) found that a delicate membrane 



