CIKCULATION OF THE SAP. 109 



in the soil is one cause of the rise of sap in the 

 plant is shown when plants are fertilized with 

 strong liquid manure. The strength of the manure 

 may not directly injure the plants, but its density 

 often prevents its absorption, and as a result the 

 plants wilt, though the roots are surrounded by the 

 fluid. Numerous erroneous opinions concerning 

 the circulation of the sap may be found in Kieth's 

 "Botanical Lexicon," and for a more complete 

 account of the causes which lead to the rise of the 

 sap the student is referred to Sach's or one of the 

 other modern works on physiological and struc- 

 tural botany. 



