182 A TEXT-BOOK OF BOTANY 
and the best exposure is not obtained. The mosses have 
made still further progress in developing an erect branch 
upon which leaves are spread out to the light and air freely 
in all directions. All this advance has been made by the 
gametophyte, which in the mosses has reached the best 
position for leaves and hence for food manufacture. How 
progress in this direction is carried further by the higher 
plants will be seen in subsequent chapters. 
