370 ANNUAL OF SCIENTIFIC DISCOVERY. 



of rain and a deficiency of foliage operate in the same manner to check the 

 formation of woody tissue, and to promote the development of fruit. 



From this theory many practical inferences may be deduced, in regard to 

 the culture of forests, orchards, and vineyards. The pruning of fruit trees 

 should be wholly regulated in accordance with the opportunities which their 

 geographical position gives them for receiving supplies of rain. The prun- 

 ing of forest trees should be confined to the removal of decaying branches. 

 If trees are to be felled in summer, the operation should be performed, not 

 after a long period of dry weather, but after copious rains, when, by the con- 

 stant evaporation from the leaves, the sap contains little organic matter 

 unconverted into wood. 



OX THE MOTIONS OF CERTAIN WINDING PLANTS. 



The following are the results of a series of observations on the motions 

 of certain winding plants (i. e., the common Lima bean, Phascolits lunatus, 

 L., and the common Morning-glory, Convolvulus purpureus, L.), made by 

 Prof. W. H. Brewer, of Washington College, Pennsylvania, and communi- 

 cated by him to S Hitman's Journal, March, 18-39. 



1st. That during the day, winding plants, like others, grow towards the 

 light. 



2cl. That they possess the property of turning towards some solid sup- 

 port. 



3d. That this is more manifest by night than by day, and the most so on 

 cool nights following hot days. 



4th. That this is not controlled by any influence of light or its absence, 

 exerted by the support. 



5th. That heat is the controlling cause, and that such plants will only turn 

 (unless it be accidentally) towards a support, the temperature of which is 

 higher than that of the surrounding air. 



6th. That the color and material of the support exert no influence further 

 than that they influence the radiation and absorption of heat ; and, 

 7th. That when such plants are in actual contact with some support, the 

 tendency to wind spirally around it is much greater than they manifested in 

 order to reach it. 



In the Proc. of the American Academy (Vol. iv., p. 98), August 1838, we also 

 find the following communication on the same subject, by Prof. Asa Gray, 

 of Cambridge. 



As much as twenty years ago, Mohl suggested that the coiling of tendrils 

 " resulted from an irritability excited by contact." In 1850 he remarked that 

 this view has had no particular approval to boast of, yet that nothing better 

 has been put in its place. And in another paragraph of his admirable little 

 treatise on the Vegetable Cell (contributed to Wagner's Cyclopaedia of Physi- 

 ology), he briefly says: "In my opinion, a dull irritability exists in the stems 

 of twining plants and in tendrils." In other words, he suggests that the 

 phenomenon is of the same nature, and owns the same cause (whatever that 

 may be) as the closing of the leaves of the Sensitive-plant at the touch, and 

 a variety of similar movements observed in plants." The object of this note 

 is to remark that the correctness of this view may be readily demonstrated. 



For the tendrils in several common plants will coil up more or less promptly 

 after being touched, or brought Avith a slight force into contact with a foreign 

 body; and in some plants the movement of coiling is rapid enough to be 



