INBREEDING AND CROSSBREEDING IN SEED DEVELOPMENT 97 



embryos resolves itself into the discovery of means of duplicating the un- 

 known but presumably special nutritive functions of the normal endosperm. 

 Two possibilities suggest themselves in this connection. One is to determine 

 natural sources of the special metabolites produced by the endosperm and 

 then add these materials to the nutrient medium. Van Overbeek (1942) ob- 

 tained significant improvement in the growth of small Datura stramonhim 

 embryos by supplying them with unautoclaved coconut milk. Blakeslee and 

 Satina (1944) later reported that the coconut milk could be replaced by un- 

 autoclaved malt extract. The other possibility is to cultivate the embr>^os 

 artificially in association with actively functioning endosperm tissue. Cur- 

 rent findings offer some encouragement that the latter procedure may prove 

 efficacious. 



Dr. Nancy Ziebur, working in our laboratory, recently has shown that 

 the growth of very young embryos of common barley (0.3-1.1 mm. long) 

 may be greatly improved by surrounding them on a nutrient agar medium 

 with aseptically excised endosperms. The basic medium employed permits a 

 satisfactory growth of older barley embryos but does not yield transplantable 

 seedlings from embryos shorter than about 0.6 mm. except in conjunction 

 with endosperms. Coconut milk and malt extract are ineffective with barley 

 embryos. Water extracts of fresh barley endosperms gave positive, although 

 smaller effects than the intact tissue. Further exploration of the living endo- 

 sperm as a source of nutrients for very young, excised embryos should prove 

 rewarding. The interrelationships of these two tissues in the juvenile seed 

 give strong credence to this approach. The success which has so often at- 

 tended efforts to grow older embryos artificially on rather simple media may 

 have blinded us to the fact that the young embryo, divorced from the endo- 

 sperm, may have quite different requirements. 



