1 9 8 THE NA TURE- S TUD Y RE VIE W 



Injured Sycamores. Last year it was reported in several botanical 

 journals that the leaves of the sycamore trees had been injured by frost. 

 Later it was stated on the authority of prominent botanists that early 

 the trouble was not due to frost but rather to the attacks of a fungus. In 

 the Report of the Missouri Botanical Garden, Dr. Von Schrenk states that 

 the leaves were killed by the severe frosts. This explanation seems more 

 reasonable because the injured trees were scattered over a wide territory. 

 However, it is certain that a fungus does grow on the leaves, and it is diffi- 

 cult to decide whether frost made conditions favorable for the fungus or 

 whether the fungus itself killed the leaves. 



Bird Migration. In the April and May numbers of School Science and 

 Mathematics, Professor Walter of Brown University has contributed an 

 interesting series of articles on theories of bird migration. It is interesting 

 to note that the following explanations have been offered for migration: 

 Instinct, magnetism, semi-circular canals, sense of direction, landmarks, 

 and follow-the-leader. Professor Walter is inclined to think that an 

 adequate explanation for the path of migration is found in the temporary 

 leadership of some individual within sight or hearing of the others who 

 knows at least a fraction of the way by experience and strikes out a safe 

 path by means of landmarks. As to why birds migrate there are theories 

 based on temperature, premonition, short days and food supply as expla- 

 nations of why birds go south; and instinct, homesickness, a desire to 

 disperse, seeking nestling food or safe nesting sites are offered as explana- 

 tions of why birds go northward in the spring. In summarizing the whole 

 matter, Professor Walter concludes that in spite of the great mass of 

 interesting theory and observation we not only do not know why birds 

 migrate but as yet we do not know how they migrate except in a general 

 way. For example, the naturalists from Aristotle to the present day have 

 failed to find where the swallows pass the winter. "Until the store of 

 facts as to why birds migrate has greatly increased, we can only delight 

 ourselves with interesting explanations as to why birds migrate, acknowl- 

 edging the problem unsolved." 



Nature-Study Exhibit. At the next meeting of the New York State 

 Science Teachers' Association to be held at Syracuse during the Christmas 

 vacation there will be an exhibit of materials, apparatus, charts, aquaria 

 and other things that biology and nature-study teachers find useful. The 

 exhibit will be made up of the things actually in use by the teachers of the 

 State. One afternoon will be spent examining and explaining the exhibit. 

 Prof. O. C. Kenyon, of Syracuse, is president of the Association. 



American Health League. The Committee of One Hundred, of the 

 American Association for the Advancement of Science, on National Health 

 is organizing the American Health League in furtherance of the cause for 

 which the Committee of One Hundred was originally appointed, namely 

 the betterment of the national health. The annual dues willbe$i.oo 

 to $5.00 per year and the official organ, American Health, will be sent to 

 members free of expense. The first number of that journal has recently 

 appeared. As a suggestion of the kind of big problems with which the 

 American Health League will deal, we take the following from a letter 

 recently sent to members : 



