CONIFE RALES 81 



in Larix and Pinus never more than a single one has been ob- 

 served to become distinct from the neighboring cells. 



In our figure of a mother cell of Pinus Laricio imbedded in 

 nucellar tissue (Fig. 63), it is apparent that it is surrounded by 

 a rather definite zone of cells, two to four layers in depth, which 

 give evidence of breaking down. After endosperm formation 

 is somewhat advanced, this investing zone becomes differentiated 

 into two distinct regions, an outer layer of tabular, almost empty 

 cells, and an inner region of polygonal cells with densely stain- 

 ing contents. It is this appearance which has sometimes led to 

 the impression that a definite tapetum surrounds a sporogenous 

 mass. The most usual mistake, however, is to regard the dis- 

 tinct mass of polygonal cells as endosperm cells, overlooking the 

 comparatively inconspicuous embryo sac, a mistake made by 

 Hofmeister ^ and corrected by Strasburger.^* 



As the mother cell enlarges, its nucellus begins to show signs 

 of the organization which precedes the reduction division and 

 would result in the first appearance of the gametophyte. It 

 may be of interest to note that after the mother cell has begun 

 to enlarge it becomes full of starch, but by the time it has 

 reached the spirem stage for division the starch has disappeared. 

 How far the history outlined above is uniform throughout Co- 

 nifers must be left to subsequent investigation to determine. 



In Sequoia Shaw ®* has observed an interesting modifica- 

 tion. When the growth of sterile tissue at the apex of the 

 nucellus has covered the sporogenous cells with five or six layers, 

 the sterile tissue of the nucellus beneath the sporogenous region 

 begins rapid division and elongation, again placing the spo- 

 rogenous tissue relatively high in the nucellus. 



III. THE GA.METOPHYTES 



THE FEMALE GAMETOPHYTE 



The female gametophyte begins with the reduction division 

 of the megaspore mother cell. In the cases investigated, the 

 mother cells seem to be the primary sporogenous cells, which 

 form a more or less extensive group, and which, although origi- 

 nating from' hypodermal cells, have become deeply placed beneath 

 the extensively developed sterile wall tissue. The deeply placed 

 mother cells (one in Lm'ix and Pinus, usually more in Taxus 



