334 MORPHOLOGY OF GYMNOSPERMS 



perisperm. In Torreya, on the other hand, the invasion by the 

 endosperm is irregular in the extreme. It is in the season after the 

 proembryo has formed that the active invasion of the perisperm 

 begins. The extension of the endosperm into the tip of the nucellus 

 above the sac proceeds in the usual way, obliterating all of it except 

 a few peripheral layers of cells. This uniform invasion seems to be 

 due to the fact that in this apical region (the original nucellus) the 

 perisperm is not growing actively if at all. Below this small region 

 at the tip, however, the perisperm is very active and evidently resists 

 disintegration much more at certain points than at others. As a con- 

 sequence, it becomes eroded by the irregularly advancing endosperm, 

 and is left in the condition of a much dissected coast line. To the 

 casual observer this results in an appearance suggesting that the endo- 

 sperm is being invaded by plates of perisperm, but this is no more 

 true than that the promontories of a dissected coast line are advancing 

 into the sea. The suggestion of an invading perisperm is further 

 strengthened by the fact that within the perisperm bordering the 

 endosperm a dark brown and finally black band of cells is developed, 

 due to abundant food storage, but this really recedes as the endo- 

 sperm advances. 



A transverse section of the mature seed of Torreya always shows 

 a definite and deep constriction of the endosperm in the center, 

 exactly opposite the two opposed vascular strands that run up on 

 each side of the seed through the inner part of the outer integument 

 (fig. 383). This constriction is the transverse section of two opposite 

 and deep longitudinal furrows in the endosperm, and it means that 

 in this longitudinal plane the endosperm encounters the greatest 

 resistance in invading the perisperm. This most resistant perisperm 

 certainly seems to hold a very definite topographical relation to the 

 principal vascular strands, and this relation may explain the resistance. 



That endosperm is the aggressive tissue at every point, even at the 

 region of most resistant perisperm, is evident for several reasons. 

 In no case are the peripheral cells of the endosperm broken down; 

 and in no case does there fail to appear one or two layers of disor- 

 ganized cells of the perisperm in contact with the endosperm. In 

 every case, also, the peripheral cells of the endosperm appear active 

 and very vigorous, and their different appearance in regions of more 



