200 AIR-VESSELS OF THE LEAVES. 



appearances. We cannot but be aware that, 

 when a branch is gathered, the sap must soon 

 flow out of those spiral-coated tubes, which are 

 large, elastic, and, no doubt, irritable. Af- 

 ter they are emptied, air may unquestionably 

 pass through them, especially when the whole 

 weight of the atmosphere is acting, as in 

 Dr. Hales's experiments v/ith the air-pump, 

 upon so delicate a fabric as the internal 

 vascular structure of a plant, forcing its way 

 through pores or membranes not naturally 

 designed to admit it. We must also recol- 

 lect that a plant, cut even for a short time, 

 begins to lose its vital principle, after which 

 no just judgment can be formed, by any 

 experiments, concerning the movements of 

 its fluids in life and vigour. See Chapter 1. 

 These experiments of Dr. Hales therefore 

 prove no more than that the vegetable body 

 is pervious in various directions ; and per- 

 haps the only point they correctly establish 

 is, that air is imbibed through ^the bark, a 

 part known to be full of air-vessels. But the 

 seventh chapter of the Vegetable Staticks 

 contains some remarks much more to our 

 purpose. Dr. Hales there clearly anticipates 



