GENERAL PAPERS 129 
the extension of root systems is having an increasing influence 
in determining the relation of plants to the soil moisture con- 
tent. 
In light we have both the measure of the intensity of light 
by Wiesner and Clements, and recently the measurement of 
photolytic ability of light by a delicate apparatus devised by 
MacDougal. Under chemical content the recent work of 
Coville with blueberries is widely known on account of its 
publication in the National Geographic Magazine. One of 
the difficulties of this quantitative work lies in the fact that 
the factors all work together on the plant, and measurement 
taken of individual factors may not indicate the true effect 
of the same factor working with others. Livingston’s sugges- 
tion of using the living plant as an index is aimed at overcom- 
ing this difficulty. 
Along physiographic lines, Cowles’ recent work on so-called 
lakes of the Mississippi Valley, has applied the principles of 
plant succession in a very practical way. The control of mov- 
ing sand is best accomplished by application of ecological prin- 
ciples in the choice of plants for that extremely xerophytic 
habitat. 
E. Place of Ecology in an Agricultural Course of Study, 
Up to the present the method has been to use a little mor- 
phology, a chapter on plant activities, and then nine-tenths of 
the work on agricultural practice. In addition to that we 
would recommend the insertion of a section on ecological 
principles covering the content of ecology as outlined above, 
which should be general and theoretical, yet so related to ag- 
ricultural practice as to form a suitable foundation for an ag- 
ricultural course. A knowledge of these principles is funda- 
mental to any real grasp of the subject. 
In conclusion, emphasis should be laid on the fact that this 
discussion does not aim to criticise agricultural activities at 
present, but to emphasize what is now being done along scien- 
tific lines for the development of general principles underly- 
ing the practice of agriculture, and the importance of its ex- 
tension as far as possible. Secondly, to point out the oppor- 
tunity in this growing branch of botany and to urge the teach- 
ing of some brief but comprehensive study of the principles of 
ecology in all agricultural courses. 
