THE ENDOSPERM 



ie: 



observed. In Lemna Caldwell 24 states that often the polar 

 nuclei do not fuse, in which case he observed that the micro- 

 pylar polar produced some free endosperm nuclei, and probably 

 the antipodal one also. In Limnocharis, one of the Alismaceae, 

 there is also no fusion (Hall 50 ), since no antipodal polar nucleus 

 is formed, and all the endosperm, which eventually fills the sac, 

 is derived from the micropylar polar 

 nucleus. In Casuarina, according 

 to Trenb, 12 there are no antipodals 

 or polar nuclei, and the endosperm 

 is formed before fertilization and 

 independently of any fusion (Fig. 

 67, B). It should be stated, how- 

 ever, that in a recent study of Casu- 

 arina by Frye 59 abundant endo- 

 sperm was found before the first 

 division of the egg, but probably 

 not before fertilization. For exam- 

 ple, the same investigator 56 found 

 in Asclepias sixteen and thirty-two 

 endosperm nuclei before the first 

 division of the egg, but not before 

 fertilization (Fig. 75). In Piper 

 and HecTceria the development of 

 endosperm before the first division 

 of the fertilized egg is even more 

 extensive. Johnson 55 represents 

 twenty-two endosperm cells in a 

 single section of Piper (Fig. 76) 

 and the egg has not yet divided. 

 Not a little confusion has arisen 

 by assuming that fertilization and 

 the first division of the egg are 

 practically simultaneous. In any event, the formation of endo- 

 sperm without antecedent fusion is clear enough in some cases, 

 and indicates that while fusion usually serves to stimulate 

 growth and cell division it is not an absolute prerequisite. In 

 certain orchids N~awaschin 36 states that the polar nuclei do not 

 fuse, but in this case no endosperm is formed. 



In this connection the experiments of Shibata 57 on Mono- 

 12 



Fig. 75. — Asclepias Cornuti. Large 

 development of endosperm before 

 division of fertilized eg-g : a, an- 

 tipodals ; e, egg ; s, synergids ; x 

 ■750.— After Frye.m 



