Ecological investigations upon the germination and early growth of forest trees ecologicalinves00boer Year: 1916 Germination of Forest Trees ^7 The foregoing tables show the effect of soil depth upon root and stem development for the same species and ages of stock. In the case of stem development in all species except Quercus ruhra, the height of the stem increases with increase in soil depth. The increase in length between the deep soil and the shallow soil is not very great, i. e., in the pines it is never over cm. and in Robinia it is never over cm. In Quercus rubra the smallest
Ecological investigations upon the germination and early growth of forest trees ecologicalinves00boer Year: 1916 Germination of Forest Trees ^7 The foregoing tables show the effect of soil depth upon root and stem development for the same species and ages of stock. In the case of stem development in all species except Quercus ruhra, the height of the stem increases with increase in soil depth. The increase in length between the deep soil and the shallow soil is not very great, i. e., in the pines it is never over cm. and in Robinia it is never over cm. In Quercus rubra the smallest height growth is in the shallow soil but the greatest height growth is in the medium deep soil. It is interesting to note that in all cases the greatest total length of stem and root together is in the plants grown in deep soil. As is to be expected the length of the tap root is materially- decreased as the soil depth decreases. In Pinus pondcrosa the tap root is 2^/^ times longer, in Robinia it is 5 times longer and in Quercus it is 3 times longer in the case of the deep soil than in the shallow soil. The length of lateral roots was taken only in the case of Pinus pondcrosa and this species is representative of what took place in all the other species. In this species the total length of lateral roots increased with decrease in soil depth. In the case of Robinia this is strikingly shown in the photographs. This indicates that whether a tree has deep-seated roots or super- ficial roots depends largely upon the depth of the soil in which the tree grows. The terms ' deep-rooted species ' and ' shaUow- rooted species ' have therefore only limited significance and the real basis for these terms is in most cases the environment. In the following table are given the data upon the effect of soil moisture upon root and stem development: The Effect of Soil Moisture upon Stem and Root Development Conifers and Hardwoods Degrees Stem Measurements Pinus pondcrosa 2 Mos.,! 3 Mos., Cm. I Cm.
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