278 



Methods in Plant Histology 



In rather long, narrow embryo-sacs, a cell wall is likely to follow 

 even the first division of the endosperm nucleus, so that the endo- 

 sperm is cellular from the beginning. Ceratophyllum, Monotropa, 

 and Verbena will furnish material of this type. 



In large, broad embryo-sacs, the formation of endosperm is 

 almost sure to be initiated by a series of simultaneous free nuclear 



E 



FIG. 101. Capsella bursa-pastoris: A, first division of the embryo cell; B, quad- 

 rants; C, octants; D, dermatogen has been cut off; E, differentiation into periblem and 

 plerorae of the root (the plerome cells are shaded) ; F, the periblem of the root is completed 

 at the expense of the upper cell of the suspensor; G, the mitotic figure in the suspensor 

 cell indicates that the upper suspensor cell by a second contribution is about to complete 

 the dermatogen of the root; H, plerome (shaded), periblem, dermatogen (shaded), and 

 the first layer of the root cap; fixed in chromo-acetic acid and stained in Delafield's 

 hacinatoxylin; 10 M thick. X400. 



divisions. In large sacs walls then begin to appear at the periphery 

 and wall formation gradually advances toward the center until the 

 entire sac is filled with tissue. Lilium, Peperomia, and Ranunculus 

 furnish examples of this type. 



