DEPARTMENT OF BOTANICAL RESEARCH. 81 



Nutritive Value of Food Reserve in Cohjledons, hy B. M. Duggar. 



Few if any quantitative studies have been made to measure the 

 importance and role of the cotyledons or seed-leaves in the nutrition 

 of the seedling and young plant during germination and later. In the 

 case of such seed as the pea or bean, where the cotyledons constitute 

 the entire food reserve, the common assumption is probably to the 

 effect that the seed-leaves are important during the first few days of 

 germination, or until the first green leaves are developed. 



It had seemed possible that problems of considerable interest might 

 be approached through a critical study of the food reserves, and pre- 

 liminary tests had been made with a few seeds, especially Canada field 

 peas. The latter were germinated over tap-water until the plumules 

 were well established, and the seedlings were then used in arranging 

 the usual solution cultures. As soon as the young shoots exhibited 

 considerable chlorophyll development, the seed-leaves were cut away 

 in duplicate cultures containing 10 plants each, while in another lot 

 the seed-leaves were left intact. To both lots of cultures were added 

 standard nutrient solutions containing all necessary ions, including a 

 favorable concentration of nitrate. A marked contrast in growth was 

 evident after the second day, and after 2 weeks the normal seedhngs 

 were tmce as tall and far more vigorous than those lacking cotyledons. 

 Although provided with many green leaves capable of photosynthetic 

 activity, and with an adequate supply of nitrate in the substratum, 

 the seedlings without cotyledons were greatly checked in development, 

 and at the close of the experiment it seemed doubtful if they would 

 attain maturity. 



During the summer of 1919 a more careful study has been made of 

 the effects of excising cotyledons after various time intervals up to 10 

 days after germination, or until the leafy shoot is 4 to 6 cm. in height. 

 At the same time, attempts have been made to substitute for the loss 

 of the cotyledons by adding singly to the nutrient salt solution glycocoll, 

 alanine, sodium asparaginate, urea, nucleic acid, and sodium nucleinate. 

 The best results were obtained when these substances were used at 

 considerable dilution, M/lOO for the simpler compounds and 0.1 per 

 cent for nucleic acid and sodium nucleinate. 



The data clearly indicate that a nutrient substitute for the cotyle- 

 dons has not been found. Sodium nucleinate has increased more than 

 any other compound, the growth amounts in the cultures lacking 

 cotyledons; yet the growth (green weight) of the normal seedlings in 

 salt solution alone exceeded in every case the growth in the cultures 

 containing organic compounds but ^dth seed leaves excised. Removal 

 of the cotyledons after the plants are 5 cm. or more in height has rela- 

 tively little effect. It is recognized that pure cultures must be employed 

 in further work in order to eliminate bacterial action. 



