VEGETABLE PHYSIOLOGY. 77 



swollen after rain. It affects fruits also which it renders watery 

 and insipid. It prevents the ripening of seeds, and occasions an 

 immoderate production of roots from the stem. Succulent plants 

 in particular are apt to suffer from too profuse waterings, and the 

 disease thus occasioned is generally incurable. The leaves 

 drop, even though plump and green ; and the fruit rots before 

 reaching maturity. In this case the absorption seems to be too 

 great in proportion to the transpiration ; but the soil when too 

 much manured produces similar effects. Du Hamel planted 

 some elms in a soil that was particularly well manured, and 

 accordingly they pushed with great vigor for some time ; but at 

 the end of five or six years they all died suddenly. The bark 

 was found to be detached from the wood, and the cavity filled up 

 with a reddish colored water. 



6. Flux of Juices. Some trees, but particularly the oak and 



birch, are liable to a great loss of sap, either bursting out 



spontaneously, owing to a superabundance of sap, or issuing from 



accidental wounds. Sometimes it is injurious to the health of 



plants, and sometimes not. There is a spontaneous extravasation 



of the sap of the vine, known by the name of the tears of the 



vine, which is not injurious. As it often happens that the root 



imbibes sap, which the leaves are not yet prepared to throw off 



because not yet sufficiently expanded, owing to an inclement 



season, the sap which is first carried up, being propelled by that 



which follows, ultimately forces its way through all obstructions, 



and exudes from the bud. But this is observed only in cold 



climates ; for in hot climates, where the developement of the 



leaves is not obstructed by cold, they are ready to elaborate the 



sap as soon as it reaches them. There is also a spontaneous 



extravasation of proper juice in some trees, which does not seem 



in general to be injurious to the individual. Thus the gum which 



exudes from the cherry, plum, peach and almond trees, is seldom 



detrimental to their health, except when it insinuates itself into 



the other vessels of the plant and occasions obstructions. But 



when the sap ascends more copiously than it can be carried off, 



it sometimes occasions a fissure of the solid parts, inducing 



disease or deformity by encouraging the extravasation and 



