Rushes and Sedges 181 
save that they wear no crown of buds and 
flowers. 
In some of our commonest water-rushes the 
leaves are reduced to sheaths, and they merely en- 
fold the base of the flower-stalk, which has as- 
sumed all their duties in the vegetable economy, 
besides fulfilling its own. In the skin of this 
doubly-useful flower-stalk there are many stomata, 
and beneath the skin are cells filled with chloro- 
phyll, so that the whole surface-tissue transpires 
and digests, as do the green parts of foliage leaves. 
Though the flowering stems of most rushes are 
filled with pith, their tubular leaves are often hol- 
low, and those of many species are kept in shape 
by an interesting little contrivance. 
If you draw one of these leaves slowly between 
thumb and finger, compressing it closely meantime, 
you feel that there are little lumps or knots in its 
inner substance. And if you split it lengthwise 
with a penknife you find that there are green gird- 
ers extending across the internal hollow and placed 
at regular distances apart (Fig. 48). The members 
of the family which bear such foliage as this are 
called ‘‘knotty-leaved rushes.” 
Their structure furnishes an answer to the me- 
chanical problem ‘‘ devise some economical means 
