AIR-VESSELS OF THE LEAVES. 151 



met with, which lives there." I have no doubt that 

 this shrimp feeds on the other insects and worms, and 

 that the same purposes are answered in this instance as 

 in the Sarraceni<e. Probably the leaves of Dionaa 

 mmcipula, as well as of the Drosera, Engl. Bot^ 

 t. 867 869, catch insects fora similar reason. 



I proceed to consider the effects of Air and Light 

 upon vegetables. 



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

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

 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 time ; and as these 

 two acute and laborious philosophers pursued their in- 

 quiries without any mutual communication, their dis- 

 coveries strengthen and confirm each other. Their 

 books have long served as magazines of facts for less 

 original writers to work with. From their remarks 

 physiologists 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 understood was not correct, because air 

 is conveyed no further than the lungs of animals : but 

 without this hypothesis no use could be found for the 

 supposed longitudinal air-vessels. 



The observations of Dr. Hales come next in order 

 to those of Grew and Malpighi. By means of the air- 



