Kraemer: Color in plants 85 



potassium nitrate, potassium iodide, iodine, potassium cyanide, etc. 

 These chemicals were supplied to the plants through the soil, 

 beginning with a strength of I part of chemical to 10,000 parts of 

 water. The strength was gradually increased until that of 1 part 

 of chemical to 1,000 parts of water was reached. It was found 

 that most of these chemicals could be supplied in this strength 

 every five days for some months without injury to the plants. In 

 other words, each plant could be supplied with 75 milligrams of 

 chemical every five days without injury. With the exception of 

 solutions of iodine and potassium iodide, and of potassium cyanide, 

 it was found that a plant in a six-inch pot could be supplied with 

 as much as 300 milligrams of chemical, an equivalent of 150 c.c. 

 of a solution containing 1 part per 500 every five days. It was 

 also found that plants growing in garden soil could be treated with 

 a stronger solution of chemical than those growing in either sand 

 or artificial soil. Plants which would stand treatment with a solu- 

 tion of potassium cyanide, 1 part to 1,000 parts, when growing in 

 garden soil, were killed by a solution of this strength when grow- 

 ing in sand or an artificial soil. 



Results of color-control experiments 



So far as I have been able to see, the treatment with the color- 

 control solutions has not produced any marked effects. Some 

 slight changes have been noted, but these could perhaps be 

 ascribed to other causes as well as to the solutions. For instance, 

 it was noted that in yellow roses supplied with aluminum and 

 potassium sulphate the leaves and stems were slightly reddish 

 and the flowers a deeper yellow than others, while those supplied 

 with potassium hydrate were paler than the type. In the case of 

 the La France rose plants supplied with iron citrate and citric acid 

 the petals were of a uniform pink color. 



The inner petals of plants supplied with iron malate and malic 

 acid were pale in color, while the inner petals of plants which 

 were supplied with either formic acid, ammonium nitrate, or iron 

 salicylate and salicylic acid were of a deep-pink color. In the 

 case of maroon roses, the petals tended to a deep purplish-red 

 when treated with potassium cyanide or potassium nitrite ; to a 

 dark-red when supplied with phosphoric acid, iron and ammonium 



