AKD 



323 



In these specimens the gain varies according to the amount of 

 foliage exposed to the air, and the consequent loss by transpira- 

 tion, all tending to establish the general conclusion that the re- 

 tention of freshness visible to the eye, or the variable amount of 

 loss or gain as proved by the balance, depends solely upon the 

 respective conditions of "supply and demand." 



7. On the Absorption of Dew. 



In the following experiments the leaves were gathered between 

 4 and 5 o'clock in the afternoon of September 10th, 1878. They 

 were then exposed at an open window to the full light of the sun 

 until it set. After two and a half hours the herbaceous ones 

 showed obvious signs of loss of water, having become more or less 

 flaccid. The loss was not visible in the case of the coriaceous 

 leaves. They were all weighed at 7 P.M. A bright moonlight 

 night followed, and an exceedingly heavy dew began to form at 

 7 p.m. The specimens were all spread out upon a grass-plot. 

 At 7 a.m. on the 11th, before the sun was visible, in consequence 

 of a very heavy mist, the specimens were carefully dried with a 

 soft cloth so as to remove all trace of dew with which they had 

 been entirely covered. They were then weighed. In every case 

 there was an actual r/ain, as seen in the following Table. But 

 besides the proof afforded by the balance, the stems and leaves 

 had perfectly recovered the freshness and rigidity which tbey 

 had lost on the previous evening. 



Gain 



per cent. 

 Tilia *lG-40 



Quercas 640 



tiambucus (old leaf ) 15*58 



„ (young leaf ) 3*56 



Geranium 1132 



Urtica 27*31 



Mercurials 14*50 



Tussilago 31*56 



Grass 3500 



Hyacinthus 2*56 



Iiumex 16*66 



Senecio 8'41 



Fagus 24*05 



Philadelpkus 8*33 



Gain 

 per cent 



Viburnum 6*8-1 



Bryonia (old leaf) 16*40 



„ (young leaf) 10*31 



Buhus 14*28 



Carduus 1071 



Nepeta 8-89 



Malm 9*09 



Ligustrum ^'^ 



Pulmonaria 8*42 



Trifolium 31*16 



Syringa 10*60 



faxus 1-94 



Berberis 0*57 



Aucuba (young shoot) 2*20 



>/ 



Finding that I could imitate dew very exactly by means of the 

 " 8 pray," I adopted this plan, so as to apply what I call » imita- 



