314 



EMBRYOGENESIS IN PLANTS 



in three successive passages, and this may be indicative of a self-dupli- 

 cation, or autocatalytic reaction, such as occurs in viruses, or of a new 

 formation of inhibitor stimulated by the originally injected tumour 

 extracts. Such tests as have been made of this substance indicate the 

 presence of nucleic acids. It has also been found that the embryo-sac 



Fig. 84. Datura stramonium 



Transverse section of D. stramonium 2n-ovules from injected capsules. A, Ovule 

 from untreated locule with normal embryo at the stage of 'bent torpedo.' B, Ovule 

 from locule injected with solution of 1 -0 p. p.m. RNA; slightly retarded embryo at 

 the 'advanced torpedo' stage. C, Ovule from locule injected with solution of RNA 

 100 p. p.m.; embryo retarded at the 'young torpedo' stage. D, Ovule from locule 

 injected with RNA 250 p. p.m. ; embryo retarded at the 'heart' stage and endosperm 

 partly digested. A and D are ovules from different locules but from the same 

 capsule (all x 30; after Rappaport, Satina and Blakeslee). 



contents of ovules of selfed Datura capsules contain (i) 6 times as 

 much of the same substance as is present in the ovules of an incom- 

 patible cross. Extracts of embryo-sac contents of selfed Datura ovules 

 with high nucleic acid content, as well as commercial desoxyribo- 

 nucleic and ribonucleic acids, were injected into ovules of incompatible 

 crosses, but embryo abortion still took place. Ribonucleic and 

 desoxyribonucleic acids inhibited embryo growth in selfed D. stra- 

 monium capsules : the former also inhibited embryo growth in cultures, 

 but the latter did not. The embryo-sac contents of D. stramonium and 

 D. meteloides both contain nucleic acids ; but extracts of the embryo-sac 



