48 Principles of Plant Culture. 
contain about 150,000 stomata to the square inch on its 
lower surface. 
bes (a = 
Se ay all 
Fic. 16. Showing stomata (s¢.) on leaf of the garden beet. Moderately mag- 
nified. (After Frank and Tschirch). See also Figs. 13, 17 and 20. 
The guard-cells are delicately-balanced valves which are 
extremely sensitive to external influences. They are open 
in strong light, but usu- 
x Nae KL eae 
a 265/25) ee ally closed in darkness 
a 2) and also when the 
i ) \ “ an 
I] /, ee 3 
be a es; ss [poke r 
heed Ui NN leaves are wet. The 
\ \ 4 SL that escapes 
water 
we Ne A sl 
ee P a from leaves (75), and 
gees eN the carbonic acid that 
oy ( > c enters them (62) mostly 
co eS pass through the sto- 
Fic. 17 Showing stomata (st ) on leaf of Olden- mata. The slightly 
burgh apple. Highly magnified. raised spots or dots on 
the smooth bark of the young shoots of many woody plants, 
(lenticels (len’-ti-cels)), serve a similar purpose to that of the 
stomata. 
