686 BIOLOGICAL EFFECTS OF RADIATION 



with the 8- and 10-hr. Ught periods in Momordica Charantia, Benincasa 

 cerifera, Phaseolus vulgaris, and Soja hispida. The same hght periods 

 also gave maximum absolute weight of fruits. Of these species all 

 flowered with each light period employed except Soja which flowered 

 only with day lengths of 6 to 10 hr. However, Benincasa produced few 

 fruits with a 16-hr. day, the yield being exceeded even by that of a 4-hr. 

 day. With Sinapis nigra all of the light periods shorter than 14 hr. 

 proved to be insufficient for flowering and fruiting. 



The conception of the ever-blooming or ever-bearing condition in 

 relation to the day-length factor advanced by Garner and Allard seems 

 to have been interpreted by some as being generally applicable to the 

 group of neutral or indeterminate plants. Although this group may 

 logically be considered as the chief source of ever-bloomers, the conception 

 in question has to do essentially with a rather delicate balance between 

 vegetative activity and reproduction which may be maintained by 

 suitable light periods in typical long-day and short-day plants as well as 

 in those of the neutral group. In buckwheat, which flowers successfully 

 with all day lengths from 5 hr. upward, a short day induces rapid, inten- 

 sive reproductive activity and only limited growth, so that the life cycle 

 is soon terminated. In this case the plant is an ephemeral. With a 

 long day, on the other hand, slower, less intensive reproduction is accom- 

 panied by extensive new growth, making possible a long-continued 

 process of flowering and fruiting, so that the life cycle is greatly extended. 

 In the latter case there is obviously a tendency toward the ever-blooming 

 state. In the same way, the short-day type, Viola papilionacea, which 

 produces its blue spring type of blossom in response to a short day, will 

 continue to produce this type of blossom for a prolonged period when 

 exposed to a favorable intermediate light period, but ceases to do so 

 with longer daily illumination. It has been suggested that in nature the 

 narrower seasonal range in the daylight period which occurs in low 

 latitudes is especially favorable to the phenomenon of ever-blooming. 



Schaffner (62, 63) has made extensive study of the effect of day length 

 on sex reversal and related structural abnormalities in Cannabis sativa L., 

 Zea Mays, and other species. Beginning July 1 and extending over a 

 period of 10 months, semimonthly plantings of hemp were made in the 

 greenhouse to ascertain the effects of the seasonal change in the daylight 

 period on sex reversal in staminate plants. A very perfect fluctuating 

 curve was obtained ranging from zero reversal in the late spring and 

 early summer plantings to 100 per cent reversal for the November 

 plantings. On November 1 plantings of certain forms of Zea Mays, 

 100 per cent of the plants will show under suitable conditions some 

 degree of female expression in the tassel while spring and early summer 

 plantings normally show only pure staminate tassels. When the female 

 state is established in the main stem, the internodes become decidedly 



