GROUPS OF TISSUES, OR TISSUE-SYSTEMS. 37 
hairs, which may be simple or variously branched. The 
most important of these hairs are those which clothe so 
abundantly the young roots of most of the higher plants, 
and to which the name of Root-hairs has been applied 
(Fig. 22). These are composed of single cells, which have 
very thin and delicate walls, and are the active agents in 
the absorption of nutritive matters for the plant. Some- 
times the terminal cell of a hair becomes changed into a 
ad 
“i 
Fie. 28.—Giandular hairs of Chinese Primrose in several stages of develop- 
ment. Magnified 142 times. 
secreting cell and manufactures a gummy or resinous sub- 
stance. Such hairs are called Glandular Hairs and are com- 
mon on many plants (Fig. 23). 
45. Breathing-Pores (stomata, singular, stoma): consist, 
in most cases, of two specially modified chlorophyll-bear- 
ing cells, called the guard-cells, which have between them 
a cleft or slit passing through the epidermis (Fig. 24). 
These openings are always placed directly over interior 
intercellular spaces. 
