199 



Thus a comparatively very slight development of HoS is found and it 

 must be assumed therefore that, if large amounts of H.S are formed in 

 marshes and other places, they must owe their origin to a reduction of sul- 

 fates in the soil, conditioned by the organic substances present. 



Pagel^ and Oswald summarized the results of their investigations on 

 such reduction processes in the substances of marshes and found that, in 

 the absence of air, sulfur metals occur, as well as hydrogen sulfid, and 

 that, together with this reduction of the sulfates, ammonia is set free from 

 the marsh substances containing nitrogen. The authors do not state defi- 

 nitely whether these substances are produced only in the absence of air, but 

 in their production may lie the harmful quality of stagnant water. 



The Burning of Plants in Moist Soil. 



In summers, remarkable because of great temperature extremes, it has 

 been observed that on hot, clear windy days, plants of rapidly growing, large 

 leaved crops, such as hops, wilt greatly, particularly when grown in damp 

 places. The lower and middle leaves of plants growing in damp hollows 

 are sometimes seen to turn yellow and brown at the edges and partially to 

 dry up so that they can be rubbed to a powder in the hand. These specimens 

 have been partly burned by the sun. The noticeable feature is that the 

 burning takes place directly on those places in the field, in which, through- 

 out the whole year, sufficient moisture is present, while in higher, drier 

 portions, still more exposed to the wind, the plants usually suffer less. My 

 comparative experiments- throw sufficient light on such cases. They prove 

 that plants, which from the beginning produce their roots in a soil contain- 

 ing much water or even in water cultures, evaporate much more water per 

 square centimetre than do plants of the same strain grown under conditions 

 exactly similar except with a lesser water supply. It is an interesting but 

 not very well-known phenomenon that many of our cultivated plants from 

 very different families grown under optimum conditions, in producing one 

 gram of mature, dry substances, evaporate approximately equal quantities 

 of water,, — indeed the transpired water varies from 300 to 400 g. in amount. 

 If the plants grow in localities which, hke soils with an impervious subsoil, 

 constantly have a great deal of water at their disposal, a constant nutrient 

 solution will be present in the interstices of the soil, more or less highly con- 

 centrated according to the soluble materials present. If the concentration 

 exceeds the amount favorable for the plant species, the plant grows less 

 vigorously, remains short-limbed, small-leaved, but usually dark green. If 

 the concentration is exactly right, the growth is very rich and luxuriant 

 and the absolute water requirement is very great, but is small if reckoned per 

 gram of dry material produced. Under such conditions the plant finds the 

 soil water of great value. In excessively damp places, however, it often 

 happens that the soil solution is poor in different nutritive substances. 



1 Landwirtsch. Jahrb., VoL VI, Supplement, p. 351. 



- Sorauer, Studien iiber Verdunstung. Forschungen auf dem Gebiete der 

 Ag-rikulturphysik, Vol. HI, Parts 4 and 5, pp. 43 ff. 



