THE FOREST ORGANISM. 



213 



anywhere in the north woods. In general, it is true that mixed for- 

 ests, Fig. 57, i. e., those having a variety' of species, grow on good 

 loamy soiL The great central, deciduous Atlantic Forest grew on such 

 soil until it was removed to make room for farms. On the other hand, 

 pure stands — i. e., forests made up of single varieties — of pine occupy 

 poor sandy soil. Within a distance of a few yards in the midst of a 

 pure stand of pine in 

 the south, a change in 

 the soil will produce i 

 dense mixed growth of 

 broad-leaves and coni- 

 fers. 



The soil in the for- 

 est is largely deter- 

 mined by the forest it- 

 self. In addition to 

 the earth, it is cum- 

 posed of the fallen and 

 decayed leaves and 

 twigs and tree trunks. 

 altogether called tl;e 

 forest floor. It is 

 spongy and hence has 

 the ability to retain 

 moisture, a fact of 

 great importance to 

 the forest. 



Fig". 56. Virj,'-in Stand of h'ed Spruce. Wliite 



Mountains, New Hampshire. (/. S. Forest 



SeTT'icr. 



MOISTUIil^. 



Some trees, as black ash and cypiess, Fig. 58, and cotton gum, 

 Fig. 59, grow naturally only in moist places; some, as the pinon and 

 mesquite, a kind of locust, grow only in dry places; \\hile others, as 

 the juniper and Douglas fii', adapt themselves to cither. Botli excess- 

 ively wet and dry soils tend to diminish the number of ]<inds of trees. 

 In many instances the demand for water controls the distribution alto- 

 gether. In the Puget Sound region, where there is a heavy rain-fall, 

 ■the densest forests in the world are found, whereas on the eastern 

 «lopes of the same mountains, altho the soil is not essentially different, 

 <here are very few trees, because of the constant droulh. 



