866 BIOLOGICAL EFFECTS OF RADIATION 



50 in. distance from the lamp caused the most leaves to develop, but they 

 were smaller than those of controls. Cultures under vita glass at 50 

 or 100 in. had fewer leaves than those under quartzlite at 50 in., but more 

 and slightly larger leaves than control cultures. For Cucumis, vita 

 glass and 50 in. distance proved superior for stem elongation, but the 

 control plants had more leaves. For Ipomoea quartzlite and 100 in. 

 distance proved best for stem growth, but quartzlite and 50 in. were 

 equally as good as quartzlite and 100 in. for leaf number, and both 

 were better than controls. To illustrate the effect of the same irradiation 

 treatment on three different sets of plants, the results of irradiation 

 through vita glass at a distance of 50 in. may be cited. With Zea Mays 

 at first the control plants grew taller, but during the last few days the 

 rayed plants grew very rapidly and surpassed the controls. Rayed 

 stalks were larger in diameter, rayed leaves outnumbered control leaves 

 and were larger. With Nicotiana, however, the observations pointed 

 toward a retardation of growth, though there was no evidence of burning. 

 With Ipomoea, little difference was noted between rayed and control 

 plants, although the rayed plants had more leaves. 



Such results point far more likely to differences resulting from inherent 

 variations of the plants themselves coupled with environmental varia- 

 tions of one type or another not taken into account. Certainly we 

 should hesitate to attribute such varied effects solely to one variable 

 under the conditions used in her experiments. Miss Eltinge's conclusion 

 that "each plant has its own ultra-violet requirement for best growth 

 which can be determined only by experiment" rests upon the assumption 

 that the ultra-violet was the only variable in the test plants as compared 

 with the controls. This obviously was not the case. So long as plants 

 can be grown from seed to seed in the total absence of ultra-violet radia- 

 tion and without showing any marked injury or any difference from plants 

 receiving such radiation, it is doubtful whether we can legitimately 

 speak of "ultra-violet requirement of plants." 



Another series of experiments from the laboratory in which Miss 

 Eltinge worked has been reported by Fuller (28, 29; Wynd and Fuller, 

 126). In many respects his methods resemble Miss Eltinge's except 

 that Fuller restricted his work to tomato and cucumber plants, both of 

 which he claims were decidedly "stimulated" by ultra-violet. This 

 stimulation, according to the author, manifested itself in increased height, 

 greater number of leaves, greater fresh weight and dry weight, and 

 increased ash content and calcium content of treated plants over con- 

 trols. The results of the major experiment were statistically analyzed, 

 but unfortunately the author did not take into account, in this analysis, 

 the fact that the conditions under which his test plants were grown 

 varied over those of the controls, not only in the quality of ultra-violet 

 they received and to which all results are attributed, but also in intensity 



