172 MORPHOLOGY OF ANGIOSPERMS 



ferent, the subsequent stages of endosperm development result 

 in all kinds of intergrading conditions, as will be shown later. 

 Even when the endosperm begins with free nuclear division, 

 a rudimentary plate often appears, suggesting derivation from, 

 an endosperm in which nuclear division was followed by cell- 

 formation. 



The history of the development of endosperm initiated by 

 free nuclear division is nearly identical, in most cases, with 

 the history of the female gametophyte in Gymnosperms, modi- 

 fied, of course, by the presence of a developing embryo. It is 

 an interesting fact, also, that the early stages in the develop- 

 ment of the endosperm bear a striking resemblance to early 

 stages in the development of the embryo of Cycadales and some 

 other Gymnosperms. There is the same simultaneous nuclear 

 division, often the parietal placing, and later the appearance of 

 cell walls. 



The primary endosperm nucleus, usually in contact with 

 the egg, or nearly so, divides, and subsequent divisions follow 

 with great rapidity, Guignard 41 remarking that in Zea he was 

 unable to follow the course of division, and other observers call- 

 ing attention not only to the great rapidity with which one set 

 of divisions is followed by another, but also to their simultane- 

 ous character. A common form of statement is that at first the 

 free nuclei remain for a time in the vicinity of the egg, but 

 sooner OT later migrate in every direction toward the wall of 

 the embryo-sac, where they become equally distributed and 

 embedded in a lining cytoplasmic layer. The real fact, how- 

 ever, is that this apparent movement of the nuclei is due to the 

 rapid enlargement of the sac, the cytoplasm becoming more and 

 more vacuolate and finally occurring chiefly as a wall layer. 

 By this increasing vacuolation the nuclei are naturally driven 

 to the wall. In this parietal position free nuclear division con- 

 tinues, until finally walls are formed and a layer of parietal 

 cells is organized. 



These first walls usually " cut out " only one nucleus in 

 each cell, but in some cases (Corydalis cava, Staphylea pinnata, 

 Armeria vulgaris, etc.) Strasburger 4 noted that two to four 

 nuclei might be enclosed by a cell wall, but that they afterward 

 fuse to form a single nucleus (Fig. 78). Tischler 39 has 

 recently reexamined Corydalis cava and states that when septa 



