THE LEAF 63 
developed structure enclosing the stem in a kind of 
sheath. This is especially noticeable in grasses. In 
some cases the leaf base swells out into a cushion called 
the Punvinus which acts as a sensitive organ enabling 
the leaf to react to external stimuli. This is the case 
for example with many of the Leguminosae. 
Fig. 39.—Branch of a young plant of Acacia melanoxylon, showing 
Phyllodes, a,b. (From ‘‘ Thomé’s Botany ”’.) 
In many plants the leaf base bears a pair of out- 
growths called SripuLES. These may be small and 
brown, their chief function being to protect the leaf when 
in the bud. In other cases they are much larger, and 
assist the leaf-blade in its functions. If they are pre- 
sent the leaf is said to be STIPULATE, and if absent 
EXSTIPULATE. 
