CHAPTER VII 



THE PERMEABILITY OF PROTOPLASM 



THE YEAST CELL. 



VERY numerous researches have shown that protoplasm is 

 freely permeable to some substances, and practically im- 

 permeable to others. That yeast cells (see Table XXV.) 

 should yield a sap the electrical conductivity of which is 

 C oxl0 5 =742, whereas the beer from which they were 

 removed affords the value C <> x 10 5 = 146, shows clearly how 

 impermeable these cells are to electrolytes. But to alcohol 

 they are freely permeable, also to glucose, as this is the 

 source of the alcohol which is formed inside the cell. 

 Paine's investigations on this subject have already been 

 mentioned in the preceding chapter. 



THE SECRETORY ACTIVITY or COLOCASIA LEAVES AND 



OF THE PITCHER OF NEPENTHES. 



Other cells appear to be completely impermeable to 

 both electrolytes and sugars. As an instance of this may 

 be cited the examination by Dixon and Atkins of the liquid 

 secreted by the leaf -tips of Colocasia antiquorum. When in 

 a warm saturated atmosphere the leaves give a continuous 

 succession of small drops from the extreme ends. These 

 may amount to several per second under favourable con- 

 ditions. A large quantity of this liquid was collected on 

 various occasions in the greenhouses of the Botanic Gardens 



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