278 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



zygote is transverse (Fig. 150 A, B). The terminal cell ca and the 

 basal cell cb both divide transversely to give rise to a four-celled 

 proembryo (Fig. 150C-F). The four tiers may be designated from 

 below upward as I, V , m, and d. Now I and V divide by vertical 



Fig. 150. Development of embryo in Nicotiana. {After Soueges, 1922.) 



walls oriented at right angles to each other to give rise to octants, 

 while m and ci divide transversely to produce d, f, n, and n' (Fig. 

 150 G-H). By subsequent divisions the tier I gives rise to the 

 cotyledonary portion, V to the hypocotyl and to the periblem and 



Fig. 151. Development of embryo in Lobelia arnoena. (After Hewitt, 1939.) 



plerome of the root, and d to the root tip. The remaining cells/, n, 

 and n' produce the suspensor. 



Hewitt (1939) has recently given a very full account of the em- 

 bryogeny of Lobelia amoena, which also belongs to the Solanad type. 



