BY LEAVES. 155 



the Willow-herb, or Epiloblum, and the Conferva, a 

 minute branching cotton-like vegetable which grows 

 ni putrid water, and the production of which, in w ater 

 become foul from long keeping on ship-board, Dr. 

 Priestley judged to operate principally in restoring that 

 fluid to a state fit for use. 



Dr. Ingenhousz, pursuing Dr. Priestley's inquiries, 

 found light to be necessary to these functions, and 

 that, in the dark, leaves gave out a bad air. He ob- 

 served moreover that fruits and flowers almost invari- 

 ably gave out a bad, or carbonic, air, but more espe- 

 cially in the dark. He probably carries his ideas, of the 

 deleterious effects of this air on animal life, too far; for 

 no mischief has ever happened, as far as common ex- 

 perience goes, to persons sleeping in apple or olive 

 chambers, neither do the inhabitants of the confined 

 huts in Covent-garden market apparently suffer, from 

 living day and night among heaps of drying herbs. 

 Mischiefs have unquestionably arisen from flowers in a 

 bed-room, or any other confined apartment, but that 

 is to be attributed to their perfumed effluvia. So the 

 bad effects, observed by Jacquin, oi Lobelia long'ijior a 

 on the air of a hot-house, the danger incurred by those 

 who sleep under the IManchineel-tree, Hippomauc 

 Mancinella^ or, as it is commonly believed, under a 

 Walnut-tree, are probably to be attributed as much to 

 poisonous secretions as to the air those plants evolve. 



Dr. Ingenhousz introduced leaves into glass jars 

 filled with water, which he inverted in a tub of the 



