CONIFERALES (PINACEAE) 



255 



but is the mother cell, as in angiosperms. It seems more probable 

 that in most cases mother cells are "picked out" directly from an 

 undifferentiated mass of cells. In Widdringtonia (159) there is a 

 remarkable early differentiation of the nucellus into peripheral and 

 central regions, suggesting to Saxton that the central group of 

 cells may be sporogenous; in fact, in a later paper (176) he speaks 



76 



277 



278 279 



Figs. 276-279. — Larix europaea: fig. 276, longitudinal section of young ovule, 

 showing megaspore mother cell and tapetal cells, and at the left the beginning of the 

 integument (March i) ; fig. 277, the mother cell has divided; fig. 278, the row of mega- 

 spores, the innermost of which is functioning; fig. 279, the beginning of free nuclear 

 division within the functioning megaspore; all XiSo. — ^After Strasbueger (25). 



of "64 megaspore mother cells." In any event, only one of them 

 was observed to function as a mother cell; although in the very 

 similar Callitris two endosperm-filled sacs were observed lying in 

 contact. 



The number of distinct mother cells is variable. For example, 

 in Pinus and Larix, and probably in all the Abietineae, the mother 

 cell is usually solitary. Among the Taxodineae the mother cells are 



