232 Nichols, A morphological study of Juniperus communis var. dcpressa. 



nuclei the outline of the original nucleus disappears, and the 

 surrounding layer of cytoplasm and starch presses in and invests 

 the two daughter nuclei. The latter grow rapidly and enter upon 

 a brief period of rest (flg. 107). 



Shortly after the completion of the first segmentation division 

 the daughter nuclei divide (fig. 108), giving rise to four resting 

 nuclei which are usually arranged in a tetrad, as shown in fig. 109. 

 There is no rule as to the position of the spindles of this division 

 with respect to the axis of the archegonium, and in this, as well 

 as in the following division, the spindle is of intra-nuclear origin. 

 Fig. 110 represents the third free nuclear division (the fourth 

 dividing nucleus appears in the next section). In this figure the 

 chromosomes have obviously split longitudinally, although they are 

 just being oriented at the equator. After the Organization of the 

 eight nuclei which result from this division wall formation usually 

 takes place, as already described by Noren (1907) in the European 

 form, and in this respect Juniperus agrees with the Abieteae and 

 Cupresseae thus far investigated. Occasionally, however, sixteen 

 free nuclei may be formed before the separating membranes are 

 laid down (fig. 111), thus approaching the condition found in Po- 

 docarpusiGo'k.QY 1902) and Cephalotaxus (Coker 1907, Lawson 

 1907 a) where sixteen are normally produced. 



Of the eight cells which are usually cut off by the formation 

 of walls the three or four which will give rise to the embryo lie 

 at the base of the archegonium, while the remaining cells form a 

 well defined tier above these. The latter are not entirely enclosed 

 by walls, being exposed above to the cytoplasm of the egg, and 

 they soon divide, giving rise to two tiers of cells (figs. 112, 113). 

 Of the cells thus formed those of the upper tier constitute the 

 rosette, and, as in most conifers, they never become enclosed above 

 by a wall. The cells of the lower tier are the suspensors, by the 

 elongation of which (fig. 114) the embryo is pushed deep into the 

 endosperm. Simultaneously with the cell division just described 

 the cells of the embryo proper usually undergo division (fig. 112). 

 The further development of the embryo has not been followed by 

 the writer. 



Sunimary. 



The buds which give rise to the staminate cones are formed 

 durin g the summer of the year preceding pollination. 



The archesporium originates from one or more hypodermal 

 cells at the base of the sporophyll. 



The tapetum and the inner layer of the sporangium wall are 

 both derived from the outermost cells of the archesporium, while 

 the outer layer of the wall — the only layer present in the mature 

 sporangium — is developed from epidermal cells. Thus the inner 

 layer of the wall is more closely correlated to the tapetum than 

 to the outer wall-layer. 



