Gbeenhouse Notes. 155 



to influence the plants, especially bj^ drawing or bending them towards 

 it. This heliotropism was most marked in the blue field, somewhat 

 less in the orange or amber field, and a trifle less in the red. A week 

 after the lamp was moved, this influence was manifest; but at this 

 time neither the plain screen nor the naked light seemed to have made 

 an impression upon the lettuce plants. Three weeks after the moving 

 of the light, however, decided differences had developed in the various 

 fields. The plants in orange or amber light were the largest and best ; 

 these were followed, in order, by those in the red, blue, plain and 

 naked sections. The naked light had now begun to injure the plants 

 seriously, a phenomenon which has been repeated throughout our 

 experiments from the first. Early in January auxanometers, for meas- 

 uring the hourly growth of plants, were started under the naked light, 

 and in the red, blue and orange fields, at equal distances from the arc. 

 The machines were set in motion upon the fifth of January, each being 

 attached to the tip of a growing leaf about an inch and a half in 

 length. On January eighteenth all the machines were changed onto 

 new leaves. During January the lettuce was making a heavy 

 growth. The house had been kept very cool previous to this time 

 and the plants had grown rather slowly, although they were in the 

 best of condition throughout the experiment. The variety was 

 Simpson Curled. The accompanying table (page 156) is a graphic 

 representation of the auxanometer readings. The bars show the 

 growth in the different fields for the hours specified, magnified — 

 to render it more readable — about three times. The number of hours 

 of electric within the specified time is shown at the extreme right. The 



