196 FIELD OATS. 



Jouve," bulliform cells. They are found in all grasses 

 that roll and unroll their leaves. These cells when 

 they lose part of their moisture contract and roll up 

 the leaf, which again expands upon their regaining it. 

 This movement reduces the amount of surface available 

 for evaporation, and is a safeguard for the plant. It 

 will be remembered that the moss leaf accomplishes 

 the same result, but without a specialized apparatus. 



t5 Etude anatomique de quelques Graminees, 1870, p. 320. 



