AIR-VESSELS OF THE LEAVES. 163 



shrimp, with a protuberant back, sometimes met with, 

 which hves there."— I have no doubt thai this shrimp 

 feeds on the other insects and worms, and fhat the same 

 purposes are answered in this instance as in the Sarrace- 

 nies. Probably the leaves of BiorKsa muscipula, as well 

 as of the Droserc^, Engl. Bot. t. 867—869, catch in^ 

 sects for a similar reason. 



I proceed to consider the effects of Air and Light up- 

 on vegetables. 



Dr. Grew, by the assistance of the microscope, de 

 tected a quantity of vesicles full of air in the leaves oi 

 plants, as also the spiral-coated vessels of their stems, 

 which last he and all other physiologists, till very lately, 

 considered as air-vessels likewise. Malpighi made the 

 same observations about the same lime ; and as these 

 two acute and laborious philosophers pursued their m- 

 quiries without any mutual communication, their discov- 

 eries strengthen and confirm each other. Their books 

 have long served as magazines of facts for less original 

 writers to work with. From their remarks physiolo- 

 gists have theoretically supposed that leaves imbibed 

 air, which the spiral vessels were believed to convey all 

 through the plant, in order that it might act on the sap 

 as it does on the animal blood. The analogy thus un- 

 derstood was not correct, because air is conveyed no 

 further than the lungs of animals ; but without this hy- 

 pothesis no use could be found for the supposed longi^ 

 tudinal air-vessels. 



The observations of Dr. Hales come next in order t» 

 those of Grew and Malpighi. By means of the air-pump, 

 gn instrument much in use in his time, Hales obtained 



