no The Plant World. 



We have, finally, to consider the suggestive lines of work 

 inspired by De Vries' mutation theory, and the re-discovery of 

 Mendel's work. It is not necessary to call attention to the 

 great influence which both the Mutation theory and the Men- 

 delian law of heredity have had upon the work both of botanists 

 and zoologists during the past decade. It must be admitted, 

 however, that as yet the results obtained by the numerous 

 students of this latest fashion in biological investigation have 

 hardly been commensurate with the expectations of the earlier 

 disciples of De Vries. Nevertheless, the careful study of varia- 

 tion, stimulated by these important theories, has been very 

 usefid in reducing to definite form many phenomena long 

 recognized in a vague way, but never before clearly formulated. 



The tendency of any striking new theor}' to draw away 

 from the older and perhaps more humdrum lines of work a large 

 number of students is a familiar phenomenon, and perhaps 

 some lines of morphological work have suffered of late from the 

 desertion of older workers, and the natural tendency of the 

 younger students to attack the latest problems presented to 

 them. It may be safely assumed, however, that there is plenty 

 of work still to be done along the lines of the older morphology, 

 and the verv creditable showing of the work of American mor- 

 phologists during the past twenty-fi\-e years makes one hopeful 

 that in the years to come the students of morphology in America 

 will not fall behind their record of the past generation. 



Sta njord Lhi iversity. 



STUDIES IN SOIL PHYSICS, III. 

 Soil water and tme Plant.* 



E. E. TREE. 



The purely inorganic aspects of the occurrence of water in 

 the soil and its movements therein were discussed in the pre- 

 vious paper of this series. It remains to notice the more vital 

 matter of the relation of this soil water to the plant by which 

 it is used and for the life of which it is essential. Of the con- 



♦Published by permission of the Secretary of AKricultuie. 



