142 PROCESS OF NUTRITION. ^ CHAP. Ill, 



lated by Du Hamel ; who having observed under 

 some Orange-trees a saccharine substance some- 

 what resembling Manna, found upon further invesj. 

 tigation that it had fallen from the leaves.* Some- 

 times it is resinous, as on the leaves of the Cistus 

 creticuSy from which the resin known by the name 

 of Labdanum is obtained, by means of beating it 

 gently with leathern thongs to which the exudation 

 adheres ;-f- as also on the leaves of the Populus 

 dilatata, or Lombardy Poplar, the exudation from 

 which Ovid in his metamorphosing flights regards as 

 the tears of Phaeton's sisters, whom he transforms, 

 as it is supposed, into this species of Poplar.^ 

 Their tears were now gum. The leaves of Frax- 

 inella or Dictamnus albus are also said to be often 

 covered with a sort of resinous substance. And 

 after a hot day, if the air is calm, the plant is even 

 found to be surrounded with a resinous atmosphere, 

 which may be set on fire by the application of the 

 flame of a candle. This, as I think, was the dis- 

 covery of a daughter of the celebrated Linnaeus. 



The cause of this excess of perspiration has 

 not yet been altogether satisfactorily ascertained ; 

 though it seems to be merely an effort and insti- 

 tution of nature to throw off all such redundant 



* Phys. des Arb. vol. i. p. 130. f Voyage de Tournefort 



I Smith's Introd. p. 189. 



Inde flaunt lachrymae, stillataque sole rigescunt 



De ramis elcctra novis, quse lucidus amnis 



Excipit, et nuribus inittit gcstanda Latinis. Ovid. Met. ii. 



