32 BOTANICAL GAZETTE [july 



3. The elaborate studies of the structure of roots are marked in 

 the main by great freedom of inference as to the functions of these 

 structures. There would seem to be need of further evidence, 

 experimental or otherwise, to give a more certain foundation for the 

 statements as to function. 



4. It seems evident that extension of root systems should be 

 interpreted in the light of the structure and function of the roots in 

 question. The length of a root is of little importance unless we 

 know how much of it is functioning for the plant. Great length, 

 also, or closeness of branching, may have very different causes and 

 effects in different species or under different conditions, and so a 

 very different meaning to the plant. 



Root systems of dune plants 



GROWTH HABITS OF ROOT SYSTEMS 



Methods. — From the consideration of the literature, it becomes 

 evident that the extension of root systems means very little ecologi- 

 cally unless interpreted in the light of function and of probable 

 causes of that extension. Studies which include simply the extension 

 of root systems, without considering the conditions of their develop- 

 ment and in some way evaluating the absorbing power of their 

 different parts, omit a large part of the significant elements of the 

 problem. For these reasons it seemed better not to attempt to 

 study the extension of the root systems of all possible plants found 

 on the dunes, but to confine the attention more intensively to a 

 few species. Within the limits of the present paper it will be pos- 

 sible to stud}' only the development of roots in relation to the 

 factors of their environment. This can best be done by beginning 

 with the germinating seed and tracing the probable course of 

 development with the influence of the environmental factors always 

 in mind. From this viewpoint length and weight of roots would be 

 of less importance than the determination of a "normal" root sys- 

 tem and the interpretation of the modifications actually found. 

 The question of structure and function, while equally important, 

 cannot be considered in the present paper, but must be left for 

 future study. 



