350 



INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



origin are also found in Atraphaxis. Of the two embryos seen in 

 the embryo sac on the left in Fig. 190C, one has obviously originated 

 from a synergid. 



Fagerlind's (1944) recent study of some apomictic species of 

 Elatostema has also revealed some interesting features of a similar 

 nature. Briefly, the polyembryonate condition is due to one or 

 more of the following causes: (1) the occurrence of multiple embryo 



A * G 



Fig. 197. Polyembryony in Elatostema. A, E. eurhynchum; embryo sac with two 

 embryos, one arising laterally. B, upper part of embryo sac, showing three 

 embryos, two of which are lying somewhat horizontally. C,D, older ovules, show- 

 ing two embryos. E, ovule, showing two embryos at micropylar and one at chalazal 

 end. F, E. acuminatum; compound embryo sac formed by fusion of two sacs. 

 Embryo sac on left shows two well-developed embryos, and that on right shows two 

 smaller embryos. G, E. pedunculosum; two adjacent embryo sacs, each with 

 normally developed embryo at micropylar end. (After Fagerlind, 1944-) 



sacs in the same ovule (Fig. 197 G), (2) the formation of embryos 

 from synergids and antipodal cells (Fig. 197 B-E), and (3) nucellar 

 budding (Fig. 197jP). Sometimes the separating wall between two 

 embryo sacs dissolves so that they form a common cavity (Fig. 

 197F), and if adjacent embryos come in close contact they may fuse 

 to form masses of tissue which defy analysis in later stages. 



Twins and Triplets. When multiple seedlings arise in a species 

 in such a low frequency that it is not practicable to make a develop- 

 mental study of the embryogeny, there is a good deal of speculation 



