896 =—s oS. C. Draper— Evolution of Structure in Seedlings. 
There remains an important argument concerning which 
nothing has thus far been said. It is to be derived from the 
consideration of the rate of growth in the light series during 
various periods of the day of twenty-four hours. If the evolu- 
tion of structure in a plant in daylight is the result of the 
action of light, that evolution should occur entirely, or almost 
entirely during the day. If on the contrary it is independent 
of the light, it should go on at a uniform rate as in plants m 
the dark. 
For the elucidation of this portion of the subject, I present 
the following tables; the first of which shows the growth by 
night, to 7 A. M. of the seedlings in the dark series, com 
pared with their growth by day, 7 4. uw. to7 P.M. The mea 
surements were taken from the sixth to the twentieth of the 
month, the day on which growth ceased in the dark series. 
Table II.—Seedlings grown in the dark. 
Night growth. Day growth. 
No. 1 122 inches, 14 inches. 
No. 2 133. ** 13> 
No. 3 1g « 11g ¢ 
No. 4 128 « ne 
Average, 12§ ‘© Average, 12% “ 
The total day growth and night. growth under these circum 
stances are nearly equal, though there is a slight excess 2 
favor of the night, amounting as the table shows, to % of 4? 
inch in 12 inches. ; 
In Table IV. the growth of the light series is given in the 
same manner, by day and by night, for the same time, viz: 1 
June 20th. The thermometric and hygrometric conditions 10 
0th series were very similar, as indicated by the dry and wet 
bulb thermometers suspended in the vicinity of each set of 
