CONIFERALES (PINACEAE) 263 



sionally multinucleate), and this binucleate or multinucleate condition 

 persists in the permanent tissue, as if the last stage of other forms 

 were omitted in Widdringtonia. 



The development of the archegonium follows the same course 

 as that described for Cycadales and Ginkgoales. The archegonium 

 initials, selected usually from the superficial micropylar cells of the 

 endosperm, become recognizable by their size at various stages in 

 the development of the endosperm tissue. In some cases they are 

 differentiated almost as soon as wall-formation has occurred in the 

 micropylar region; in other cases they are not evident until the endo- 

 sperm tissue has reached an advanced stage of growth; and between 

 these two extremes there is every intergrade. There is evident 

 among Pinaceae, and notably among Coniferales in general, a tend- 

 ency to develop archegonia earlier and earlier in the ontogeny of the 

 gametophyte, a tendency that expresses itself somewhat irregularly 

 but none the less clearly, and that reaches its extreme expression in 

 the appearance of archegonium initials immediately after the free 

 nuclear stage of the gametophyte (as in Torreya). The significance 

 of this tendency may be appreciated when it is remembered that among 

 Gnetales it has resulted in the differentiation of eggs during the free 

 nuclear stage of the gametophyte, and therefore in the elimination 

 of archegonia. This tendency will be discussed more fully later, 

 in connection with a general consideration of evolutionary tendencies 

 among gymnosperms. 



An initial cell, recognizable usually in May or June, enlarges 

 considerably and then divides by a periclinal w^all into the primary 

 neck cell (outer) and the central cell (inner) (figs. 289, 290). The 

 primary neck cell divides by an anticlinal wall, and this division may 

 be followed by others, the number of cells in the archegonium necks 

 of Pinaceae being very variable. The adjacent cells of the endo- 

 sperm grow faster than the neck cells, so that the neck opens in the 

 bottom of a funnel-shaped depression, known as the archegonial 

 chamber. 



The central cell begins a remarkable increase in size, and about 

 it a definite nutritive jacket of endosperm cells becomes differentiated, 

 which may be referred to as the archegonial jacket orjapetum, and 

 which must not be confused with .he nucellar tapetum that invests 



