EFFECTS OF LIGHT INTENSITY 733 



increased from 20.83 to 29.55 per cent, (d) Peptide nitrogen decreased 

 from 34.06 to 27.52 per cent. 



He interpreted these results as indicating that acid amides increase 

 at the expense of certain amino acids such as tryptophane and tyrosin, 

 while amino acids increase at the expense of the polypeptides. 



Nightingale and Schermerhorn (71) grew asparagus shoots, from 

 root stocks of plants formerly grown in light, in quartz sand irrigated 

 with nutrient solutions with and without nitrogen. Some of the plants 

 were grown in the greenhouse and others in darkness. Plants in darkness 

 not only absorbed nitrates but from them built up higher nitrogen com- 

 pounds, a process which was accompanied by a decrease in carbohydrates 

 in the root. Nitrates were abundant in the absorbing roots of both the 

 plants in light and of those in darkness but were not found in the shoots 

 except after active growth had ceased. In the plants grown without 

 nitrates, no nitrates were found; but there was a considerable amount 

 of soluble nitrogen in the shoots and a corresponding decrease in the 

 nitrogen of the root. Reid (80, 81, 82) demonstrated that seedlings 

 and cuttings could assimilate nitrates and use them to build up growth- 

 promoting substance in darkness, provided they had a high carbohydrate 

 and low nitrogen reserve. On the other hand, growth of seedlings from 

 seeds having a high protein and low carbohydrate reserve was not 

 favored appreciably by addition of nitrates to the nutrient media. 



Excised tips of roots and of shoots of corn, peas, and cotton were 

 cultured by Robbins (83) in mineral nutrient solutions containing 2 per 

 cent glucose, or levulose. The cultures were maintained under sterile 

 conditions and kept in darkness. Under such conditions considerable 

 growth took place, but practically none occurred in cultures which con- 

 tained no carbohydrates. The shoots had the characteristics of eti- 

 olated shoots — small leaves, yellow color and excessive elongation. 

 Robbins and Maneval (84) grew, in light and darkness, excised root tips 

 in modified Pfeffer's solution containing 80 and 400 parts per million of 

 autolyzed yeast, and also in solutions containing 2 per cent glucose. 

 Those in the light survived longer (one for 149 days) and produced more 

 tissue, as measured by length of main axis, number of secondary roots, 

 and total dry weight. 



Wilson (121) cultivated vetch seedlings in darkness on a sterile agar 

 nutrient medium containing sugar. After 2 days these test cultures 

 were inoculated with the nitrifying bacterium, Rhizohium leguminosarum. 

 After 36 days the plants were examined for nodule formation. Nodules 

 were found in all cultures but were more prevalent in those supplied with 

 0.5 and 1.0 per cent saccharose. The plants without sugar died first, 

 but even with these one nodule was found. The media containing 

 0.5 and 1.0 per cent saccharose proved to be more favorable for the growth 

 of etiolated seedlings than those containing the same percentages of 



