lM2 



iinicUls which, at'lcr tlu'v ha'l dried out, had hccn subse(iiiently soaked 24 

 hours in water, and found that the tine root ends were still shrivelled 

 despite the soaking. The character of most Ericaceae, as moor and heath 

 plants, is shown by the fact that (with the exception of a few varieties) 

 they thrive best in a freely watered, easily drained, aerated soil. In growing 

 plants in small pots the need of roots for air must be given the greatest 

 possible consideration. The Ericas soon become root bound. The plants 

 easily become sour in large pots. The Erica and Azalea drop their leaves 

 when dried out. It is wrong, however, to try to repair the previous mis- 

 take by setting the pot in water and. after soaking up the earth, to place 

 the plants in closed cases in order to reduce evaporation as far as possible 

 and to cause turgidity. The plants should be left, on the contrary, in their 

 customary place, but strongly shaded during the middle of the day. 



AIkans of Ovi:kcomixg Lack of Moisture in thf. .^oii.. 



If a lack of soil moisture is manifested by the failure of vegetation or 

 by its degeneration, as usually occurs more frequently in sandy soils, one 

 naturally seeks relief in irrigation when possible. This artificial supply of 

 water not only refreshes the tissues, but also, by dissolving the nutritive 

 substances in the soil, it is possible for the plant to utilize and distribute 

 these. 



Irrigatiox. 



W ith the fre(|uent lowering of the ground water le\el, irrigation be- 

 comes a vital question and an acquaintance with the results of Konig's' 

 investigations on the effects of irrigation water is interesting. One learns 

 accordingly that when a meadow is being irrigated the water loses much of 

 its nutritive material and appreciably more during the warmer seasons, than 

 in the colder ones. This loss, however, is not true of all nutritive substances. 

 If the carbon dioxid content of the irrigation water rises, the calcium and 

 magnesium nearly always increase instead of decreasing. As in the case 

 of carbon dioxid, this quantity seems to rise and to fall with the intensity 

 of the oxidation in the soil. In contrast to the above-named nutritive sub- 

 stances, potassium appears to be absorbed at any time by the soil since, with 

 irrigation, even in the winter, a slight reduction of this important mineral 

 can be proved in the water. Sodium, or rather sodium chlorid, just like 

 nitric and sulfuric acids almost always showed a slight increase during 

 winter irrigation, while during the growing season they decrease, i. e., they 

 are taken up directly by the plants. 



Konig concludes that the oxygen of the water acts as a purifier of the 

 soil by oxidizing the organic soil contents. This oxygen content varies 

 according to the kind of w^ater used in irrigation and the season. Konig 

 found it greate;st in spring, smallest in summer, increasing again in the 

 autumn. Spring w-ater is much richer in oxygen than river water w'hich 

 has passed through inhabited places. The opposite is true of the suspended 



1 Journal fiir Landwirtsehaft. .TahrR. ISSO. A'ol. 28. Part 



