The Light-Requirement of Plants. 



201 



(1) Hundreds of acorns have been planted, but there is 

 no record of one having sprouted. 



(2) The few specimens discovered are isolated from each 

 other. 



(3) The leaves closely resemble those of the shingle oak. 



(4) The cup and fruit bear marked resemblance to those 

 of the black oak. 



The author thanks Captain Holden of the Lloyd Library 

 for aid in locating the Cincinnati specimen of 0. Leana, Nutt. 

 University of Cincinnati. 



THE LIGHT REQUIREMENT OF PLANTS. 

 By Joseph V. Bergen. 



There is probably no higher authority on the relations 

 of plants to light than Professor Julius Wiesner of the Univer- 

 sitv of Vienna. He has, during many years, published import- 

 ant papers on this general subject, and in 1907 he set forth the 

 principal results of his researches in his Lichtgenuss der Pfianzen, 

 \Y. Hnglemann, Leipzig. As there are few important topics 

 in plant physiology of which most of us know as little as we do 

 about the amount of light needed by plants for successful life and 

 growth, it may be worth while to sum up for the readers of The 

 Plant World a few of Wiesner's statements and to comment 

 on some of them. 



The author defines the term Lichtgenuss as meaning sub- 

 stantiallv the light-requirement of any given species of plant. 

 The relative light-requirement signifies the fraction of the total 

 amount of light in any particular region which will enable the 

 plant in question to thrive there. For example, if a plant will flour- 

 ish in the evergreen woods of the Adirondack regionwith one-third 

 of the total light which falls on unshaded areas there, its light 

 requirement is 1-3. It is noteworthy that as a rule the light- 

 requirement increases in the higher latitudes. Acer platanoides , 

 which in Vienna, lat. 48.12 deg. N., has a light-requirement 

 ranging from 1 to 1-55, in Tromso, Norway, lat. 69.50 deg. N., 

 has a requirement of from 1 to 1-5. 



Evidently, as the author remarks, the introduction of light- 

 measurements, even if at first they may be somewhat crude, 



