FORMATION OF KALMIA PEAT. 33 



times known as " Maryland peat." This material is not a bog peat at 

 all, and since it is of very great interest in connection with these blue- 

 berry experiments, for it was the principal ingredient in a majority 

 of the successful soil mixtures used, it is desirable that the reader 

 have a comprehensive idea of its character. 



Maryland peat, as brought to the greenhouses of the United States 

 Department of Agriculture, consists of dark-brown turfs or mats, 2 to 

 4 inches thick, made up of partially decomposed leaves interlaced with 

 fine roots. It is found in thickets of the American laurel {Kalmia 

 latifol'id) where the leaves of this shrub, usually mixed with those of 

 various species of oak, have lodged year after year and the ac- 

 cumulated layers have become partly decayed. 



The nature of the deposit may be easily comprehended by means 

 of the accompanying illustrations. The photographs from which the 

 illustrations were made were secured through the courtesy and skill 

 of Mr. G. N. Collins, of the Bureau of Plant Industry. The photo- 

 graphs were made in the month of April, 1908, in a laurel thicket at 

 Lanham, Md. After one photograph was made, the layer of leaves 

 represented by it was removed and another photograph was taken 

 showing the layer immediately underneath. 



In Plate III, figure 1, is shown the top layer of the leaf deposit aS 

 it appeared in April, 1908, consisting of oak leaves of various species 

 which fell to the ground in the autumn of 1907. The next under- 

 lying layer is shown in Plate III, figure 2. The laurel leaves here 

 shown are those that fell in the summer of 1907. Laurel being an 

 evergreen, its leaves are not shed in the autumn like those of the oaks. 

 They remain on the bush until the new leaves of the following spring 

 are fully developed and then the old leaves begin to fall. It is this 

 circumstance of the fall of the oak and laurel leaves at different 

 periods of the year that enables one to recognize the different layers 

 and know their exact age. The third layer, shown in Plate IV, figure 

 1, consists of oak leaves of the autumn of 1906. This layer was moist 

 and decomposition was well started. The presence of fungous growth 

 is evident, as is also the excrement of various small animals. Myria- 

 pods, or thousand-legged worms, and the larvfe of insects must play a 

 very important part under some conditions in hastening the de- 

 composition of leaves. The fourth layer, Plate IV, figure 2, consist- 

 ing of laurel leaves shed in the summer of 1906, is in about the same 

 condition as the preceding layer. In the fifth layer, Plate V, figure 1, 

 are shown the leaves of 1905, but the layer of oak leaves is not readily 

 separable from the laurel. The rotted leaves crumble readily and 

 decomposition has so far progressed that a few oak rootlets are found 

 spread out betAveen the flattened leaves. Plate V, figure 2, shows the 

 rotted leaf layers of 1904 interlaced with the rootlets of laurel and oak. 

 It is this root-bearing layer, 2 inches or more in thickness, of which 

 54708°— Bull. 193—10 3 



