178 NATURAL HISTORY OF THE FARM 



such leaves will be found. Commingled with the leaves are 

 pieces of stems and bark and twigs. Strips of birch bark 

 long persist, being rendered well-nigh moisture-proof by 

 their abundant resin. 



Under the recognizable leaves and twigs is humus, formed 

 from those that fell earlier. It is black and full of moisture. 

 It is mingled with the top layers of the soil. As we uncover 

 the floor of the leaf-beds, we see some of the agents nature 

 uses in promoting the formation of humus: molds and 

 mildews and other fungi of many sorts, that grow in and dis- 

 integrate the plant-stuffs; snails and earthworms and mille- 

 pedes and pill-bugs and spring-tails and many insect larvas 

 that eat them. Carnivores are here, also; ground-beetles 

 and centipedes and spiders, among the lesser forms, and 

 salamanders and shrews, among those of larger size. The 

 beds of leaf-mold have a population of their own. All are 

 hastening the restoration of the useful plant materials to the 

 soil. Numberless roots are holding the humus together. 

 They never let go; this is nature's way of keeping the soil 

 productive. It is only after we have dug down through the 

 humus-stained top layers that we come to soil that looks 

 like that in the fields. 



Not in the woods alone, but also in the wild meadow and 

 on the prairie, nature practices admirable economy in the 

 use of her soil-riches. Gravity aids in the enrichment of 

 the lowlands, but in spite of gravity the soil of the hills 

 improve as time runs on and wild crops grow upon them. 



In holding what is'gained the deep-rooting forest-cover is 

 not more useful than is the turf -forming ground-cover her- 

 bage. Great and small are colaborers. in nature's plan. 

 Her method is conservation with [use — the fullest possible 

 use — the use that brings the greatest good to the greatest 

 number, and that insures the' continued welfare of a teem- 

 ing population. 



