1921] Abstracts and Reviews 109 



weed (Mikania scandens), wild Hibiscus {Hibiscus Moscheutos) and 

 the common garden variety of radish (Scarlet Globe) are members of 

 this class. For the sake of convenience these plants have been termed 

 long day plants, indicating that they attain sexual reproduction suc- 

 cessfully when the days are relatively long. 



By the use of electric light of low intensity to increase the relatively 

 short duration of illumination of the winter days, results in line with 

 those obtained when the summer day has been shortened, were secured. 

 Thus, soy beans and cosmos blossomed weeks and months after the 

 controls enjoying the normal duration of illumination of the winter 

 days. 



It is evident that the duration of the daily illumination in itself is 

 of primary significance in controlling the course of development to- 

 ward or away from the flowering stage or sexual reproduction. 



Experiments with several so-called late varieties of soy beans in the 

 field, planted at intervals from April to August, have shown that the 

 shortening of the period from planting till the first appearance of 

 blossoms, is dependent upon the seasonal length of day to which the 

 successive plantings have been subjected. 



In the light of these results it is believed that the natural distribu- 

 tion of plants is governed more or less directly by the seasonal length 

 of day which obtains for the different latitudes of the earth from the 

 equator to the poles. 



From the evidence at hand it will be seen that the stature and 

 season of flowering of certain plants is dependent upon a favorable 

 length of day, and this may actually be a most important limiting fac- 

 tor in determining crop yields in many instances. In other words, the 

 time for propitious seeding to obtain maximum yields may be governed 

 very largely by the length of day to wdiich the crop will be exposed. 



Since it has been shown that certain plants respond wdth a definite 

 behavior to certain day lengths, the term "photoperiodism" is sug- 

 gested to designate this response. 



Teaching of Geometry. By Archibald Henderson, Professor of Pure 

 Mathematics, University of North Carolina. 



If this paper (a pamphlet of 49 pages, Univ. N. C. Extension Series 

 No. 33) simply followed the usual treatment of books on "The Teach- 

 ing of Geometry," it would not call for special mention; but, as it 

 strikes a distinct note, and gives many fresh discussions not found 



