310 EMBRYOGENESIS IN PLANTS 



Capsella: it gave better growth results than a nitrogen-equivalent com- 

 plete aminoacid mixture. Ammonium lactate could not serve as a 

 substitute for aminoacids. In contrast with glutamine, asparagine 

 yielded low growth values, the embryos being characterised by an 

 abnormally rapid and strong production of starch. 



It appears that some aminoacids, such as tyrosine and glycine, are 

 unsuitable for the culture of Capsella embryos. Although glutamine, 

 menlioned by Street (1949) as the prevailing amide in the seedlings of 

 Brassicaceae (Cruciferae), gave very good growth results, Rijven 

 considers that there may be yet other aminoacids, or related compounds, 

 that promote embryonic growth. Steward and Thompson (1950) have 

 stated that there are still twenty unidentified substances indicated 

 by paper-chromatography which belong to this category. The failure 

 of asparagine, a homologous compound, to promote growth of Capsella 

 embryos is the more remarkable when we remember how important it 

 is in protein synthesis in Pisitm, Lupinus and other Leguminosae. 



The addition of bios, purine derivatives, and other growth-regulating 

 substances, gave negative results. Indoleacetic acid gave a small but 

 significant effect, stimulating growth at 0-001 p. p.m. and inhibiting it 

 at concentrations greater than 1-0 p. p.m. Other investigators also 

 have found that the addition of various growth-regulating substances 

 has little effect on the growth of embryos in vitro. Sanders (1950) 

 obtained negative results with them using Datura embryos, and 

 Rappaport, Satina and Blakeslee (1950) have reported that nucleic acid 

 is inhibitory. With Pisiim on the other hand, growth-regulating 

 substances have been found to have promoting effects, but this was in 

 the post-germinal phase. 



Large, post-germinal embryos in culture yielded no evidence of 

 precocious germination. The germination characteristically took place 

 when the osmotic value of the medium was lowered. In fact, there are 

 important differences in the cultural requirements of pre-germinal and 

 post-germinal embryos. 



EXPERIMENTS ON OLDER EMBRYOS 



The study of older embryos not only carries its own interest but may 

 contribute towards an understanding of the younger and less accessible 

 stages. Contemporary investigators are concerned with the culture of 

 mature embryos, with the conditions required for the germination of the 

 seeds of different species, some of which present difficulties, and with 

 an analysis of the associated physiological process. The information 

 obtained from some of these studies is of practical importance in 

 horticulture. 



In a study of the 'hormonising' of seeds, Kruyt (1952) grew excised 



