312 GROWTH OF PLANTS 



that the C/N ratio varied broadly, both in short days where no flowering 

 occurred and in long days where flowering always occurred. 



Salvia plants were gro\vn in a great range of day lengths, light intensity, 

 CO 2 supply in the air, and nitrogen supply in the soil with little variation 

 in the C/N ratio in the plants. The carbohydrate content varied from 22.87 

 to 28.19 per cent and the nitrogen from 2.04 to 3.24 per cent. Increasing 

 the nitrates in the soil from a very low level to a concentration that injured 

 the plants gave little change in the percentage of nitrogen in the plant. 

 Salvia seems to regulate nitrogen absorption regardless of the available 

 supply, as has been found by Woo ® for Amaranthus retro jicxus and by 

 Hooker and Bradford ^ for apple. Salvia is a short-day plant flowering in 

 a 5- to 15-hour day but rarely in a 17-hour day. While C/N ratio varies 

 relatively little in this plant, it is the day length and not the C/N ratio 

 that determines flowering. 



Buckwheat, which flowered on all lengths of day from 5 to 24 hours, 

 showed a great variation in the carbohydrate and nitrogen percentage in 

 the plants grown under various conditions. On the dry weight basis, plants 

 grown in a control greenhouse for 64 days in the winter of 1927 contained 

 7.94 per cent carbohydrates, while a plant grown in a 24-hour day for 33 

 days contained 39.41 per cent. Plants gro^vn in a 24-hour day for 65 days 

 contained 0.46 per cent nitrogen, while those grown in a 5-hour day for 

 69 days contained 3.44 per cent nitrogen, and those gro\vn in a control 

 greenhouse during the winter for 40 days contained 3.72 per cent nitrogen, 

 all on the dry weight basis. It is quite evident from the results stated in 

 this paragraph that buckwheat, a plant that flowers on all lengths of days 

 tested, shows no relation between flowering and the C/N ratio of the tissue. 



Chemical analyses were made of a number of other plants (cabbage, red 

 clover, soybean, cucumber, potato, ragweed, tobacco, several small grains, 

 and corn) grown under a wide range of conditions from very favorable to 

 unfavorable for high photosynthesis and nitrogen absorption. In general, 

 increasing the light intensity, day length, and CO 2 content of the air 

 increased the dry weight, the size, and the carbohydrate percentage of the 

 plants. The increases held generally for increase of day length only up to 

 a 17- or 19-hour day, but did not hold for increase in day length from a 

 17- or 19-hour day up to a 24-hour day. The failures to increase up to the 

 24-hour day may be due to the injurious effects of the artificial light used; 

 or it is possible that plants need some rest from photosynthesis even under 

 sunlight. Most of these plants showed an increase in the nitrogen fraction 

 with increase in nitrogen content of the soil; but the small grains and corn 

 seem to regulate nitrate absorption, as does salvia mentioned above. The 

 day length rather than chemical composition, or C/N ratio, determines the 

 flowering of all photoperiodic plants. Plants indifferent to day length as 

 regards flowering, flowered over a wide range of C/N ratio, as did the 

 photoperiodic plants. 



