daily periodical growth of Wheat and Barley. 1 59 



although necessary to plants, does not, on the contrary, appear 

 to be submitted to any rule of time or quantity. As to light, 

 vegetables require it of a very high degree of intensity, be- 

 fore they can arrive at certain periods of their perfect develop- 

 ment ; but it is much less necessary to their growth in length. 

 It would therefore appear of importance to compare the periodi- 

 cal motions of the growth of the young plants, with the vari- 

 ations of the internal temperature of the apartment. For this 

 purpose, the author gives a table of its variations ; but he has 

 found little or no connection between the oscillations of the 

 thermometer, and the oscillations observed in the growth of 

 the young plants. The only relation which he has been able to 

 make out between the two tables, is that presented by the cir- 

 cumstances that the first acceleration of the growth coincides 

 with the most rapid ascending motion of the thermometer, be- 

 tween eight and ten in the morning. But this coincidence does 

 not again present itself in the subsequent periods ; and even the 

 greatest acceleration which takes between two and four in the 

 afternoon, happens at the moment when the thermometer begins 

 to faU. 



The author concludes his curious memoir, by observing that 

 it is somewhat probable that these periodical oscillations of the 

 daily growth depend upon the vitality of the vegetable alone ; 

 or that, perhaps, the cause is a complex cause ; that the pe- 

 riodicity of the oscillations depends upon the vitality, and their 

 intensity upon external causes. But as it would be improper to 

 draw too positive general conclusions from the small number of 

 observations which he has made, he proposes to continue them, 

 and in the mean time lays before the public what he has been 

 able to gather on this interesting subject, in the hope of exciting 

 others to similar researches.* 



• Extract from the LinniEa, t. iv. pp. 98-113. Bib. Univers. Feb. 1829. ^ 



