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A TEXTBOOK OF THEORETICAL BOTANY 



phase and wall formation starts with the first division (Fig. 1335). The 

 arrangement of the cells formed is at first generally regular and constant. 

 Irregular cell formation supervenes at later stages. Schnarf has recognized 

 the following types, according to the direction of the first cell wall. 



Fig. 1335. — A and B, Adoxa moschatellino. Cellular 

 endosperm ; two- and four-celled stages. C, 

 Cellular endosperm in CalUtriche. D, Helobial 

 endosperm in Bittomus iimbetlatiis showing first 

 transverse division. (A and B after Lagerberg. 

 C after Jorgensen. D after Holmgren.) 



I. The primary wall is longitudinal to the embryo sac. Examples are: 

 Adoxa, Centranthiis (sometimes) and a few Dipsacaceae. In Lappula 

 (Boraginaceae) the first wall is vertical but does not reach beyond the micro- 

 pylar end of the sac. Another vertical wall follows, at right angles to the 

 first, and from these open " cells " nuclei pass down to the antipodal end 



