Development of Root Systems Under Dune Conditions

Abstract

1. The study of the literature shows that the work done on extension and development of root systems has been surprisingly little, in view of the importance of the root in the utilization of moisture and chemicals in the soil. This study also emphasizes the necessity of interpreting the extension of root systems in the light not only of structure and functions, but also of the causes of such extension. 2. The study of the habitat selected shows that dune sand as a substratum for plant growth is almost unique in uniformity of texture and in absence of mineral salts required by growing plants. It is homogeneous chemically, but contains not only old soil layers but minute streaks and patches, apparently of carbonaceous and organic origin, as well as dead plant parts, very unequally distributed. 3. The roots of dune species react differently to the elements of this heterogeneous structure, extension being increased in some species by the buried organic matter, while others seem unaffected or even inhibited by it. 4. These reactions are specific and hereditary, and may reflect the conditions under which the ancestral plants grew. They must be regarded as of great importance in the choosing of species for introduction into conditions where the humous content is uneven. 5. Giving due weight to the possibility of moisture, oxygen content, and penetrability of the sand as influencing factors, the evidence seems to point conclusively to nutrient or at least chemical influence as the cause of variability in symmetry in the extension of roots under dune conditions. 6. Under certain conditions the root apparently utilizes organic matter directly, at the expense of its shoots. Extreme lengthening and thickening of roots occurring under these conditions call into question the value of the common method of estimating plant growth by measuring the length and weight of roots.