THE ENDOSPERM 



231 



Schnarf, 1929), and Marcgraviaceae (Mauritzon, 1939) the second 

 division, and sometimes the third also, is transverse, resulting in a 

 row of four or more cells (Fig. 127). More commonly, however, 

 the second division is vertical, and subsequent walls are laid down in 

 variable planes. 



Of special interest are several members of the Sympetalae and of 

 a few families belonging to the Archichlamydeae and the Mono- 

 cotyledons, in which there is a differentiation of prominent endo- 

 sperm haustoria. The haustoria may arise at the chalazal end, or 



C D E F 



Fig. 127. Development of endosperm in Yillarsia reniformis. A, two-celled 

 stage. B,C, four-celled stage. D-F, eight-celled stage. (After Stolt, 1921.) 



at the micropylar end, or at both. Taking the simplest forms first, 

 in the Nymphaeaceae and Araceae the primary chalazal cell formed 

 after the first division of the endosperm mother cell undergoes no 

 further divisions and functions directly as a haustorium. A whole 

 mount of the endosperm of Peltandra (Goldberg, 1941), belonging 

 to the Araceae, shows several strands of streaming cytoplasm trav- 

 ersing the large vacuole of this cell. Its nucleus becomes lobed 

 and hypertrophied, and the nucleolus breaks down into a number of 

 highly vacuolated fragments. 



A similar large chalazal cell is seen in Thesium (Schulle, 1933; 

 Rutishauser, 1937) and Balanophora (Zweifel, 1939). The first 

 division of the primary endosperm nucleus, which lies in the vicinity 



