248 RESULTS OF COMPARATIVE OBSERVATIONS: BAVARIA. 



ecormons evaporation constantly ffoing on tlirongh the leaves, &e., dur- 

 ing the growing season, especially in tbe day-time, wbicb passes o£t' into 

 the air as an invisible vapor, and must be replenished from the soil 

 through the agency of the roots, or they wilt and die. The tree is, in one 

 sense, a stream of water, which during the growing season is moving 

 from the fibers of the roots through the outer body of wood into the 

 limbs and branches and into the leaves. The forests thns withdraw a 

 great amount of water from the soil and give it ofl" as vapor. In win- 

 ter the process is partially suspended, but still there is a certain degree 

 of activity in the roots. They lay up a supply of aliment in the wood 

 which serves to keep them alive at a time when grass and herbs would 

 die, and from the depth to which the roots penetrate, they are able to 

 draw water from deeper strata which never become dry, and may thus 

 be able to endure the driest seasons. 



The amount of water which plants and trees need to sustain life, de 

 l)euds mainly upon the growth and evaporation. The latter difters in 

 the same plant, according to age, size, and location, as well as condi- 

 tions of soil, amount of light, and motion of the air. We have as yet 

 no reliable results as to the amount of water which different forest 

 jilants and trees under various circi mstances lose by evaporation. This 

 is a subject which deserves our attention in the highest degree, and 

 furnishes a rich subject for forest-experimental stations. While Unger 

 found that water would evaporate three times the amount of a i>lant of 

 the same surface, Schleiden concludes^ that a forest evaporates at 

 least three times as much Avater as a water-surface of like area. Ac- 

 cording to Hartig, a forest evaporates less than free water or wet 

 earth. In hot summer days some plants will evaporate their own weight. 

 In fact, forests afford, and some species of trees more than others, a 

 kind of vertical drainage of water from the soil.^ 



With respect to the r. lative amount of water falling in the fields and 

 forests, it was found uniformly greater at the surface of the earth in 

 the former than the latter, for the manifest reason that a part was inter- 

 cepted by and evaporated from the foliage of the trees. The percentage 

 in the woods, as compared with the fields, varied in different years by 

 f-easons, i'rom 40 to 90, being on the general average of all stations, 

 and, for the whole period, least in spring and most in winter. 



Ptrccntage of rain and siw%c reacMng the earth at different seasons in the woods, as compared 

 will) adjacent fields. 



1 Baum iind Tf'ald, Leipz c, 1870, p. 46. Mnch information npnn tho movement of water 

 in plants will be found in the Sack's Text Book of Botany, y. 5'.)«-(il4, where citations to 

 other authorities will also bo found. 



- Dr. Ebermayer })roceed9 to discuss the subject of evaporation from growing plants 

 with considerable detail, citing manj- authorities. Our space does not admit of a 

 fuller consideration of the subject. 



