NOTES AND COMMENT 27 



physiology to establish some principles regarding the conditional con- 

 trol of plant processes, and the sooner we appreciate the need of 

 quantitative definition of all effective conditions in every piece of ex- 

 perimental work, the more rapid may be our progress toward such prin- 

 ciples. Since radiation (light) is a continually and irregularly varying 

 condition in nature, since it is essential to the later growth of green 

 plants but not for seed germination, and since it cannot readily be either 

 measured or controlled (excepting by its practical elimination), the 

 germination phase of plant growth offers the most promising field for 

 true experimental studies. This phase may be studied without any 

 light reaching the cultures; in other words, the radiation condition may 

 be maintained at zero intensity for practically all effective qualities. 



It is the purpose of this note to emphasize the importance of the 

 general principle brought out by Gericke, and also to emphasize the 

 possibility of really good experimentation if cultures can be kept in 

 darkness, as in the case of germinating seeds. Methods are already 

 available for the control of maintained temperatures, and probably for 

 that of the oxygen and carbon-dioxide relations. Since neither light nor 

 the evaporating power of the air are generally important influential 

 conditions in seed germination, these two environmental features may 

 be practically eliminated from the discussion, by maintaining them 

 nearly at zero intensity, when seed germination is the process to be 

 studied. — B. E. Livingston. 



Dr. W. Howard Rankin has recently published, in the MacMillan 

 Company's series of Rural Manuals, a treatise on the diseases of trees. 

 The general diseases affecting all trees are treated collectively, followed 

 by chapters on the specific diseases of all the hardwoods and conifers of 

 economic or ornamental importance in the United States. Symptoms 

 and causes are fully described and remedial measures are given so far 

 as known. There are brief chapters on tree surgery and methods of 

 spraying. References to original papers are given under each disease. 



