26o 



PLANT GROWTH SUBSTANCES 



as osmotic agents. The experiments with pairs of components lead to 

 the further conclusion that the nutritional effect of casein hydrolysate 

 may be attributed to the amino acids and phosphate. The results as a 

 whole suggest that one is dealing here with another case where the 

 determination of the amount and the type of development is not mainly 

 dependent on one specific growth requirement of the embryo, but may 

 result from an interplay of both nutritional and physical factors. 



In summarizing this discussion it will be realized that the field of 

 plant embryo growth is relatively undeveloped. A number of workers 

 have had a variety of results with different materials, and it is difficult 

 to draw from their data any conclusions as to the important factors which 

 in general influence the growth of plant embryos. Histological studies 

 have contributed an understanding of the probable functions of the 

 various seed parts in supporting and controlling the growth of young 

 embryos, but the exact chemical nature of the substances involved is 

 not known. Experiments on the inhibition of seed germination have 

 led to the discovery of a variety of ways in which the development of 

 older embryos may be controlled in nature. In vitro studies of the 

 embryos of a number of different species have shown that at early stages 

 embryos require for their nutrition not only minerals and sugar, but 

 also in some cases vitamins, amino acids, nucleic acid, and unknown 

 materials occurring in coconut milk or malt extract. And the pattern 

 of growth followed by an embryo may be influenced not only by the 

 known growth hormones, but also by amino acids and such other factors 

 as osmotic pressure. Future research in this field should include more 

 of the exploratory work just reported, but especially should attempts 

 be made to relate the effects of an apparently diverse group of factors 

 all of which play an influential role in the growth of plant embryos. 



REFERENCES 



1. Blakeslee, a. F. and Satina, Sophie, Science, 99:331 (1944). 



2. Brink, R. A. and Cooper, D. C, Botan. Rev., 13:423 (1947). 



3. Cooper, D. C. and Brink, R. A., Botan. Gaz., 111:139-153 (1949). 



4. Curtis, J. T., Am. Orchid Soc. Bull., 16:654 (1947). 



5. Evanari, M., Botan. Rev., 15:153 (1949). 



6. Haagen-Smit, a. J., Siu, R., and Wilson, Gertrude, Science, 101:234 



(1945)- 



7. Kent, Nancy and Brink, R. A., ibid., 106:547 (^947)* 



8. Nutman, p. S., Ann. Botany, N. S. 3:731 (1939)- 



