86 Kraemer : Color in plants 



sulphate, or sulphuric acid. In fact the color of the maroon roses 

 approached that of the crimson roses when treated with sulphuric 

 acid, and they also tended to singleness. 



The scarlet carnation, when supplied with any of the following 

 chemicals, showed a tendency to form white streaks in the petals : 

 iron and ammonium sulphate ; aluminum phosphate ; iron citrate 

 and citric acid. The maroon carnation, when fed with ferrous 

 sulphate, also showed this same tendency. The petals of a white 

 carnation, when the plant was fed with potassium and aluminum 

 sulphate, showed a tendency to form red streaks. 



There was a disposition on the part of the plants treated with 

 potassium cyanide to produce less chlorophyl. In the case of 

 the roses and pansies the leaves were beautifully variegated ; in 

 one of the roses growing in sand the edges of the leaves were red, 

 the veins green and the remaining portion yellow. An insuffi- 

 cient supply of iron is generally supposed to produce a paling of 

 leaves, but our observations have not confirmed this. This would 

 tend to show that in certain plants iron is not as necessary as is 

 commonly supposed. 



The chief difficulty in experiments of this kind is to achieve 

 and maintain exact control conditions. My work may now be said 

 to be approaching these conditions, and my previous experiments 

 must be regarded as more or less preliminary. It is well known 

 that, when plants grow in a soil containing excessive amounts of 

 copper or zinc, the plants take up these elements, and this demon- 

 strates that the plant will take up certain chemicals under certain 

 conditions, whether they assimilate these or not or whether they 

 are poisoned by them. Until we can establish control conditions 

 whereby we can determine the effects of each substance supplied 

 the plant on different parts of the individual plant, we shall not be 

 able to say just what is the effect of a chemical under varying 



conditions. 



In the interesting experiments of Hoffmann already referred to, 

 on the zinc violet, while he is inclined to consider that individual 

 variation may account for its variability in color, still he says that 

 possibly a difference in climate or physical character of the soil 

 may have influenced the results. While the plant has certain 

 inherent qualities or tendencies which are more or less difficult to 



