at different periods of the Day. 



113 



the Sweet Willow was on the 7th of March, when the noon day 

 observation gave .56 ; at that hour the growth of the Fig had been 

 only .08 and of the Passionflower .24, which was about the aver- 

 age ; and of the Vine only .42 which was slightly above it. The 

 greatest growth of the Passionflower was on the 14th of April, when 

 the 6 p.m. observation gave .82 which was .42 above the average ; on 

 the same day the Willow had grown .36, or .20 above the average ; 

 the Fig .09, or about the average ; and the Vine, .14 or .24 below 

 the average ! If we turn to the instances of impeded vegetation 

 we shall perceive just the same conflicting results. The slowest 

 growth of the Vine was on the 10th of April when the Noon day 

 observation amounted to only .04 to .34 below the average; at 

 that time the Passionflower had grown .34 or .11 above the 

 average ; the Fig .03 or .5 below the average; and the Willow. 14 

 or only .2 below its average elongation at that hour. 



Upon the whole then it seems that we must regard the growth 

 of plants as a far more complicated problem than is generally sup- 

 posed. The evidence that has been produced appears to show 

 that there is a regular oscillation of growth during the 24 hours, that 

 the principal developement takes place in the afternoon, (between 

 noon and 6 in the evening), and follows the smallest which occurs in 

 the Forenoon (between 6 in the Morning and noon) ; and that this 

 oscillation is not connected with light and temperature, because the 

 growth in the Forenoon is less than in the Morning (11 P.M. to 

 6 A.M.) when the temperature is at its lowest ; it may also be in- 

 ferred that thin-skinned plants grow fastest in the absence of bright 

 light, and possibly that thick-skinned plants obey an opposite law. 



But it does not appear satisfactorily that the varying rates of elon- 

 gation are, under the circumstances of the experiments now de- 

 tailed, dependent, to any considerable extent, upon fluctuations of 

 temperature, light, or moisture. On the contrary it seems almost 

 certain that some other powerful agent is in operation, the nature 

 of which we have at present no means of ascertaining. 



vol. hi. 2nd series. Q 



