50 Dr. J. C. Draper on Growth or 



various periods of tlie daj 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 in 

 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, 7 P.M. to 7 a.m., of the seedlings in the dark series, com- 

 pared with their growth by day, 7 A.M. to 7 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 III. — Seedlings grown in the dark. 



Night growth. Day growth. 



No. 1 12| inches. 14 inches. 



„ 2 131 „ 13 ,, 



„ 3 11| „ 11| „ 



,,4 12|- „ ll| „ 



Average . . 12| „ Average . . 12| „ 



The total day growth and night growth under these circum- 

 stances are nearly equal, though there is a slight excess in 

 favour of the night, amounting, as the table shows, to f of an 

 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. to 

 June 20th, The thermometric and hygrometric conditions in 

 both series were very similar, as indicated by the dry- and 

 wet-bulb thermometers suspended in the vicinity of each set 

 of tubes. 



Table IV. — Seedlings groion in the light. 



Night growth. Day growth. 



No. 5 §5 inches. 4 inches. 



» 6 8 „ 7 „ 



,,7 5i „ 41 „ 



„ 8 91 „ 8i „ 



Average . . 6| „ Average . . 6 „ 



In the average, and throughout the table, with a single ex- 

 ception, not only is the uniformity in the rate of growth during 

 the day and night shown, but the slight excess of night growth 

 found in the series kept in the dark is likewise copied. We 

 must therefore accept the conclusion, that the act of growth or 



