300 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



Leitneria (Pfeiffer, 1912) and Sassafras (Coy, 1928) the condition 

 is variable, and the first wall may be either transverse or longi- 

 tudinal. 



In Scabiosa succisa, which has been described in detail by Soueges 

 (19376), the first wall in the zygote is diagonal, dividing it into two 

 somewhat unequal cells, a and b (Fig. 172^1). The former corre- 

 sponds to the terminal and the latter to the basal cell of the two- 

 celled stage. In the next division each cell is partitioned more or 

 less transversely, producing the daughter cells c, d, e, and / (Fig. 

 1725). The following divisions do not follow any definite sequence 

 (Fig. 172C-E), but derivatives of c and e give rise to the cotyledonary 

 zone, d and the lower part of / give rise to the hypocotyledonary 



A B C D E 



Fig. 172. Development of embryo of Scabiosa succisa. (After Soueges, 1987b.) 



region, and the upper part of / to the root cap and a poorly differen- 

 tiated suspensor. The dermatogen is differentiated at an early 

 stage, but the periblem and plerome are distinguishable only after 

 the appearance of the cotyledons. 



A well-differentiated suspensor is also lacking in Cimicifuga (Earle, 

 1938). Here the first division of the zygote is transverse. The 

 basal cell, which is considerably larger, divides vertically, and the 

 terminal divides obliquely. Further divisions are slow and irregular 

 and the proembryo soon becomes a club-shaped mass, about ten 

 cells long and two to four cells broad. There is no clear line of de- 

 marcation between the suspensor and the embryo, and the cells of 

 the former are distinguishable only by their position and vacuolated 

 cytoplasm. 



In several members of the Gramineae also there is no regular 



