The Light-Requirement of Plants. 



205 



trees, are tolerant of shade, while most oaks, hickories, chestnut, 

 locust, and larch are intolerant. Wiesner gives many valuable 

 data in regard to the relative light-requirement of temperate 

 European and American and of arctic and tropical trees. A re- 

 markable instance of gradual adaptation of a leaf during its 

 development to increasing light intensity is displayed by Am- 

 herstia nobilis, a beautiful Caesalpiniaceous tree which flour- 

 ishes in the garden at Buitenzorg. The young leaves are flacid 

 and almost colorless, evidently containing little chlorophyll. 

 They hang vertically downward and are greatly sheltered by 

 the older leaves. Little by little they become firmer and as- 

 sume a green color, until at length they can withstand the full 

 glare of the tropical sun. Apparently the fully developed ones 

 in some instances receive about five hundred times as much light 

 as the youngest and most protected ones. 



Summing up a few of the good and bad points of Professor 

 Wiesner's book, it may be said to contain more detailed and au- 

 thoritative information upon the light relations of plants than 

 any other single work. It is extremely interesting and sug- 

 gestive of many lines of investigation for the plant physiologists 

 of all countries. On the other hand it does not seem to be well 

 arranged for reference, the topics discussed are not treated with 

 regard to their relative scientific importance, and the index is 

 most inadequate. A brief glossary would have aided the reader 

 who is not familiar with the author's other writings on this 

 general topic, but none is given. It would seem to many 

 botanists that Wiesner. in trying to fix the light minimum for 

 the species studied, has too readily assumed that when a plant 

 does not grow well or grow at all on the forest floor or in the shade 

 of other shrubs or herbs it fails to flourish wholly because of 

 the shade. Lack of water or of nutritive salts or even deleterious 

 substances given oil by the roots of the trees may at times figure 

 as factors in the problem. , i 



THE PRESENT STATUS OF PLANT PATHOLOGY. * 

 By Venus W. Pool. 

 For the purpose of ascertaining the opinions of pathologists 

 at the various Experiment Stations in regard to the different 



*A paper presented before the IV>tanical Seminary of the University of Nebraska' 

 May 1909. 



