206 



aeration of the soil, — is overlooked. The plants have not improved with this 

 treatment. The best results are obtained by transplanting when growth 

 starts and the application of heat to the roots to stimulate growth. 



Eichhom's^ investigations prove that fertilizing may be injurious rather 

 than advantageous with acid soil, in the presence of free humus acid. He 

 states that earths, rich in humus, which contained free humus acid, liberate 

 the acids from solutions of neutral salts. The acidification thus produced 

 is stronger than it would be without these salts and, therefore, fertilization 

 with neutral salts will increase the acid in such soils. This happens with 

 calcium phosphate or any phosphate where the phosphoric acid, or calcium 

 l)hosphate, passes over into solution. The addition of neutral potassium 

 salts, especially alkaline sulfates, favors decomposition. If the humus 

 acid is combined with a base, such acidification does not take place. The 

 addition of manure, liquid manure, etc., will act only disadvantageously 

 with such chemical decomposition and is to be avoided as are marly earths. 



Ix JUDICIOUS A\^ati:rixg. 



The frequent dying of house plants makes necessary a reference to in- 

 judicious watering. Excessive watering may be due to the fact that in- 

 experienced people assume a lack of moisture in the soil as soon as the plant 

 wilts. The fact that frequently, after watering, the plant becomes turgid 

 (luring the course of the day gives weight to this assumption. If wilting 

 follows this second turgidity, water is added until the plant is permanently 

 wilted and the roots decay. Such conditions arise especially in the autumn 

 when the more tender plants are put in conservatories with but little heat. 

 The coldness of the soil then causes the wilting. We know from a number of 

 cases cited by Sachs- that different plants require definite temperatures for 

 their roots to keep them working, i. e., taking up water. Tobacco and 

 pumpkins wilt in a soil at 3° to 5°C. ; but if the same soil is warmed to 

 12° to i8°C., the root activity is re-established. In the examples cited above, 

 when the previously watered, wilted plants become turgid during the day. 

 this result is attributed to the influence of the watering. The real cause, 

 however, was the diurnal rise in temperature of the air and of the soil, 

 caused by the sun. whereby the roots were again stimulated to take up 

 water. \\'ith the coming of night and the corresponding fall in temperature 

 below the limit at which the roots are still to take up water, the wilting is 

 repeated. The plant can therefore die of thirst even when the soil is very 

 moist, if the soil be too cold. On the other hand, in moist air, the plants 

 can remain alive a long time with wholly decayed roots, as is shown by water 

 cultures. This is also the reason why, in root diseases, symptoms of dis- 

 turbance are noticeable in the aerial organs only at a late stage. 



Another cause of the wilting becomes noticeable in midsummer. If 

 plants transpiring rapidly are exposed for some time to the hot sun and to 



1 Landwirtsch, .lahrbiicher 1877, p. 5)57. 

 - Lehrbuch der Botanik, 1st. Ed., p. 559, 



