104 James Small on 



Apart from this very extensive and ini]!ortant economic- 

 application of the eflfect of carbon dioxide on the direction of 

 growth, there are numerous other lines of scientific and economic 

 investigation in which the fact that the root is relatively acid 

 while the stem is relatively alkaline, has been overlooked. The 

 new evidence for the verity of this phenomena may prove of great 

 value in directing the attention of investigators to its obvious 

 results in experimental and observational work. 



For exam.ple, it is well known that only a fcAv plants are 

 able to grow in distinctly acid media, such as sphagnum bogs and 

 sphagnum peat ; similarly a few other plants show a very decided 

 preference for chalky soils. The continued existence of both 

 classes obviously depends upon special relations between the 

 reaction of the soil and the reaction of the roots of the plants. 



Two interesting cases of the influence of " reaction " on the 

 growth of the plant occur in the maize and the bean. The 

 ordinary maize is yellow, but A^arieties are sold which are white,. 

 e.g., Sutton's White Horse-tooth Maize. The colour is due to a 

 substance which becomes intensely yellow with ammonia vapour 

 and is changed to a colourless product by acids. The yellow 

 maize is yellow because it is, as a whole, relatively alkaline ; 

 while the white maize is white because it is in the same way 

 relatively acid. Keeping in mind that the root is acid, it is 

 interesting to note that, while in yellow maize the main root 

 aborts when it is not more than two millimetres long, the white 

 (acidic) maize produces a main root several inches long. 



A similar phenomen occurs in the bean. Broad beans Avith 

 green seed-coats give straighter longer main roots on first ger- 

 minating than do those with broAvn seed-coats. Such seedlings 

 as the former naturally stand abetter chance of successful growth 

 into m;i,ture plants. Now, the green bean is acid and the brown 

 bean is relatively alkaline. The colouring matter can be ex- 

 tracted ; it is green in acids but turns brown in alkaline media. 



