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THE AMERICAN NATURALIST [Vol. XL 



The Root Systems 



A special study of the structure and extension of the root sys- 

 tems of desert plants cannot fail to be of great interest and im- 

 portance in contributing to a right understanding of the biology 

 of these plants. Many characteristics of the desert vegetation 

 are without much question directly traceable to peculiarities of 

 the various root systems. It has been observed (Coville, '93, 

 p. 43) that the fairly equal spacing of desert shrubs is one of 

 the characteristics of their distribution. The primary cause for 

 this is presumably the struggle for water and their distribution 

 is, therefore, an expression of the mutual relationship of the root 

 systems. Again, frequently the form of the root is incompatible 

 with certain habitats, — for example a subirrigated plant would 

 find difficulty in growing where the subsoil is the rock-like calliche, 

 — and plants with such deeply penetrating roots, for instance, 

 are for this reason limited in their distribution. Tt is theoretically 

 possible, and so far as I have observed actuallv true, that those 

 plants that have a root system which is at (nu-v sujM'rficial and 

 which penetrates the ground deeplv, all other thiniis heitiu' (Hpial, 



the creosote bush, for example, wliicli lias a root svsteni of this 

 character (V. M. Spalding, :()4) i> perliaps the most widelv dis- 

 tributed of our desert shrubs. Althonoh this view of the relation 

 of the character of the root systems to the distribution of these 

 plants is advanced tentatively only, the importance of it as a 

 factor which must be taken into consideration in this connection 

 and sometime carefully studied, is very apparent. 



The root system of a specimen of Echinocactus wislizeni which 

 was 60 cm. high and 35 cm. in diameter, growing about 75 meters 

 north of the laboratory, was carefully exposed and the course of 

 its roots mapped (Fig. 4). The roots, as the figure indicates, 

 were branched very freelv. There were three main roots which 

 arose from the base of the plant not far fr(»m 10 em. from the sur- 

 face of the ground and wliieii so directed tiieir growth, and that 

 of the branches, that the area compassed by them was about 

 equally apportioned and well covered. As a rule the roots were 



