186 EXPEEIMENT STATION. [Jan. 



cult problem to determine accurately the role which texture 

 alone plays in plant distribution and adaptation. 



Humus is undoubtedly closely associated with certain eco- 

 logical features connected with the life history of plants, since 

 it furnishes an environment for various micro-organisms 

 which in some instances amount to many millions per gram; 

 and if the behavior of these organisms in culture media fur- 

 nishes a criterion for their activity in soil, important chemical 

 changes must take place. 



In endeavoring to account for the distribution of any 

 particular species of plant, one is confronted with a complex 

 problem, since there are various influences responsible for 

 distribution, and the elimination of these factors is beset 

 with difficulties. 



In some cases differences in the degree of adaptability of 

 plants appear to exist corresponding with their stages of 

 development ; for example, a seedling will die in a soil of cer- 

 tain texture, when a more mature plant of the same species 

 will succeed in thriving to a greater or less extent. 



Soil texture exerts an influence uj)on the configuration of 

 plants which may be seen even in restricted areas ; for ex- 

 ample, certain soils are especially adapted to the luxuriant 

 development of elms, and such soils exert a marked influence 

 not only upon the general type of tree, but the color, size 

 and texture of the leaves, — a feature which may be seen 

 to a similar degree in other native plants. 



Among our well-known cultivated plants there are some 

 which are influenced to quite an extent by soil texture, the 

 best known among these being tobacco. Since the texture, 

 aroma and color of the leaf is tested many thousand times 

 daily by smokers, much knowledge has been gained regarding 

 the influence of soil texture and other factors upon the growth 

 of this crop. It is well known that the crops from some soils 

 sell for two and three times as much as those grown on soils 

 of a different texture. In the development of head lettuce 

 soil texture also plays an important role. This type of lettuce 

 is largely grown on the Atlantic coast soils, which predom- 

 inate in the coarser grades of sand. When head lettuce is 

 grown in finer-texture soils it does not head up well, and little 



