ABSTRACTS AND REVIEWS 



Effect of the Relative Length of Day and Night and 

 Other Factors of the Environment on Growth and Re- 

 production IN Plants. By W. W. Garner and H. A. AUard. 



(Note: The authors have furnished by request the following ab- 

 stract of their work. Mr. AUard was assistant in Botany in the Uni- 

 versity of North Carolina in 1904-05. Both authors are now in the 

 Department of Agriculture, Washington. Their paper under the above 

 title was published in Journ. Agr. Research 18, No. 11, 1920.) 



Although the intensity of the light and the quality as regards wave- 

 length of radiation are recognized as important factors in the develop- 

 ment of plants, the present paper deals mainly with the behavior of the 

 plant in response to the daily duration of the period of light. This 

 phase of the subject of light effects upon plants appears to have re- 

 ceived little attention in the past but in the present paper sufficient 

 evidence has been accumulated to show that it has an extremely im- 

 portant bearing on the expression of plants as regards growth, stature, 

 and specialization in the direction of sexual reproduction. 



The main feature of the present paper is a demonstration of the 

 fact that with many plants, sexual reproduction in some manner is a 

 function of the relative length of the day and night. In other words, 

 by artificially shortening the summer daily illumination period 

 by keeping certain plants in a dark house for suitable periods of the 

 day, sexual reproduction or flowering is initiated. Thus, the plants 

 may be made to bloom at will, weeks or months in advance of controls 

 responding to the normal seasonal length of day. Thus, certain late 

 varieties of soy beans, namely Biloxi and Tokio, in particular, and the 

 variety of tobacco known as Maryland Mammoth, have shown them- 

 selves very responsive to such conditions. The wild aster, Aster 

 linariifolius, and other species also blossomed precociously, so to 

 speak, when the length of day was reduced to 12 hours or 7 hours, re- 

 spectively. Plants of this class may be considered short day plants, 

 since sexual reproduction has been initiated by a length of day con- 

 siderably shorter than the normal summer day which tends to promote 

 vegetative growth, until the shorter days of late summer and autumn 

 intervene to initiate flower and seed production. 



On the other hand, certain plants have consistently shown a dif- 

 ferent behavior, and have failed to bloom in response to a day length 

 of 7 hours, as obtained by the use of the dark house. Climbing Hemp 



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