64 MOONLIGHT. 



The plants on which M. Zantedeschi principally experi- 

 mented were Mimosa cUiata, Mimosa pudica, and Desmodium 

 gyrans. He always took great care to determine exactly the 

 position of the leafstalks and leaflets of the plants after they 

 had been exposed to the open air, and before they were directly 

 illuminated by the lunar rays. He thus avoided any causes of 

 error which might have arisen from the imperceptible motion 

 of the air, or from a slight change of temperature ; and he 

 satisfied himself fully that the effects observed did result 

 entirely from the action of the rays of light from the moon. 

 Without entering into minute details, it is sufficient to say 

 that the results were ascertained when the temperature of the 

 air was 70° Fahr. ; and when Saussure's hygrometer indicated a 

 medium state of humidity. Under such conditions, the leaf- 

 stalks of Mimosa cUiata were raised half a centim.etre, or about 

 four-tenths of an inch ; those of the Mimosa pudica were raised 

 one inch and two-tenths; whilst the leaflets of Desmodium 

 gyrans exhibited distinct vibrations. It was thus demonstrated 

 that moonlight has the power, jper se, of awakening the Sensitive 

 Plant, and consequently that it possesses an influence of some 

 kind on vegetation. It is true that the influence was very 

 feeble, compared with that of the sun ; but the action, such as 

 it is, is left beyond further question. This being so, the 

 question remains ; what is the practical value of the fact ? 

 It will immediately occur to the reader that possibly the screens 

 which are drawn down over hothouses at night, to prevent loss 

 of heat by radiation, may produce some unappreciated injury 

 by cutting off the rays of the moon, which Nature intended to 

 fall upon plants as much as the rays of the sun. 



Even artiftoial light is not wholly powerless. De Candolle succeeded 

 ia making Crocuses expand by lamp-light, and Dr. Winn, of Truro, 

 has suggested that the oxy-hydrogen lamp may be made subservient to 

 horticulture in the long dark days of winter. It does not, however, 

 appear that this hypothesis rests upon any experimental basis. 



The mere fact of plants absorbing water from the earth 

 would render it probable that they have some means of parting 

 with a portion of it by their surface ; but that they do perspire 



