32 VEGETABLE PHYSIOLOGY 
constructed, in which a quantity of air is slowly accumulated 
and into which the respiratory products can be discharged. 
From such reservoirs the oxygen which the cells require 
is obtained. The composition of the atmosphere in these 
chambers or lacune is not accurately known, but it pro- 
bably differs somewhat from that of ordinary air. 
These air passages 
or reservoirs are very 
conspicuous in the 
stalks of floating 
leaves such as those 
of the water-lily, and 
in the submerged 
stems of most aquatic 
plants (fig. 34). 
A somewhat simi- 
lar mechanism is 
Fig. 85. Cortex or Root, ssowine IntER- provided in the case 
CELLULAR PASSAGES BETWEEN THE CELLS. 
of terrestrial plants. 
At the time of their first formation, all the cells are 
in close approximation to each other at all points of 
their surface. This condition is, however, only tempo- 
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Sep: S860" eeae; ou 
Fic. 36.—Sgction or Lear sHowine Tin LARGE INTERCELLULAR SPACES 
OF THE MrsopHyy. 
tary; during the early stages of growth the cell-walls 
split apart at particular places, usually the angles of the 
cells. A system of intercellular spaces is thus formed 
which, as growth proceeds, become continuous with each 
