CONIFERALES (PINACEAE) 265 



said to pass from the next outer layer into the cells of the jacket, 

 and the jacket cells were often seen emptied of all their contents. 

 These details of observation have been mentioned chiefly to illustrate 

 the dangers of such interpretations when the sections are more than 

 one layer of cells in thickness. Migrating nuclei squeezing through 

 walls can often be seen by examining several superimposed layers 

 of cells. It is now known (117) that these large pits of the arche- 

 gonial jacket cells, in early stages, are closed by a membrane, which 

 is perforated only by Plasmodesmen, so that under these conditions 

 the bodily transfer of nuclei or any solid material is impossible. Just 

 what the situation is in later stages is uncertain. 



The central cell enlarges and receives food material for two or three 

 weeks, its nucleus retaining the apical position, when it divides about 

 simultaneously with the division of the body cell in the pollen tube 

 (76, 157), to form the very small ventral canal cell and the very large 

 egg (figs. 292-297). The ventral canal cell disorganizes and dis- 

 appears with more or less rapidity; while the egg nucleus begins 

 immediately a very rapid and a very great enlargement. It moves 

 toward the center of the egg, and attains a size that seems out of all 

 proportion to its original bulk and to the time involved. During 

 maturation of the egg the characteristic changes occur in the nucleus 

 which were described in coimection with the egg of Cycadales. 



The notable feature in connection with the development of this 

 archegonium, as contrasted with that of pteridophytes, is the com- 

 plete elimination of the neck canal cells. The general tendency among 

 pteridophytes is to reduce the number of these cells, and among 

 Filicales the reduction has reached the stage of a single uninucleate 

 cell; but among gymnosperms even this has disappeared, and there 

 is no trace of neck canal cells. 



The behavior and character of the nucleus of the ventral canal 

 cell, which is sister to the egg, has attracted attention. Usually its 

 disorganization is very prompt, often beginning before it returns to 

 the resting stage; and afterward its disorganized remains may be 

 seen in various stages, even to the early stages of embryo-formation. 

 The nuclei of the ventral canal cell and of the egg are at first exactly 

 similar, apparently differing only in the quantity of cytoplasm involved 

 in each case, and suggest that the ventral canal cell is an abortive 



