2 _ ple of little ante-chambers before reaching the great 
130 THE BREATHING PORES OF LEAVES. 
der the surface, or raised above it, or surrounded by a rit 
smaller cells with thinner walls than the remaining epiderm 
Immediately under the stomata are empty spaces, of i 
form and varying size, called breathing rooms. They are 
nection with, and form a part of the intercellular space whic 
ramifies through the entire structure of most tissues. 
dowed with all the peculiar properties of their natural st 
were they always existent in their peculiarities, only sm: 
the leaf was younger? Or, have they grown out of a sing 
by the process of subdivision and after growth? Do théy 
to the epidermis, or to the chlorophyl bearing tissues 
Two examples, studied in their structure and history, will 
some light on these questions. 
Gasteria verrucosa, of the aloe family shows, seatte 
the surface, small, thick-walled squares with a deep cavity 
centre (Pl. 3, fig. 6). These squares fall at the juncti 
little cone in the middle. In the centre of each square, 
tom of its cavity, can be seen a narrow slit. Various $ 
will show more of the structure. Pl. 3, figs 7 and 8 repre 
horizontal slices seen from below ; i.e. inverted on the 
the microscope. The razor in fig. 8 has passed through 
cells, and in fig. 7 just beneath them. In fig. 7 you see, 
ing through the green pore cells, the thick-walled s¢ 
was so plain in the surface view. The vertical sections, 
10, show the thick outer wall of the epidermis and the li 
or protuberances seen in the middle of the cells in fig. 
9 it will be perceived that the opening between the p 
not a plain straight-walled cavity, but that the two ¢ 
in the middle, and again by means of horns or protub 
nearly in contact above and below, thus making as i 
room. The striped portion under the pore cell in fig: 
sents a thickening of the cork layer which has formed 
lies on a little lower plane than the rest of the dra 
square cavities above the pore cells may be called the 
of the stomata. When you drop a little of Schultz’ 
