74 A TEXTBOOK OF GENERAL BOTANY 
TRICHOMES 
Some of the epidermal cells of ‘most plants grow out singly 
or, less frequently, in groups, to form appendages which are 

Fig. 59. Branched hair 
of Callicarpa caudata. 
(x 50) 
lar or multicellular, 
known as trichomes or hairs. Frequently 
the trichomes lose their protoplasmic con- 
tents and become filled with air. The 
young leaves of many plants have tri- 
chomes which are shed as the leaf becomes 
older. Cotton consists of long unicellular 
hairs which grow from the epidermis of 
cotton seeds. 
Trichomes exhibit a great variety of 
form and vary from small protuberances of 
the epidermal cells to complex, branched, 
multicellular structures (Figs. 59, 60). 
Even the simple unbranched hairs show 
great variety. They may be unicellu- 
straight or curly, project straight from 
the epidermis or lie parallel with it. When they lie against 
the surface of the leaf and all point in the same direction, they 
produce a silky appear- 
ance. The methods of 
branching exhibited by 
the trichomes are very 
diverse. Among the 
most beautiful forms 
of trichomes are those 
known as scales. These Fyg. 60. Top and side views of stellate hair 
are flat structures hav- of Callicarpa erioclona. (x 850) 
ing short central stalks 
(Fig. 61). Scales are sometimes found so close together as to 
form an almost complete covering over the surface of a leaf. 
A dense covering of dead trichomes has a tendency to restrict 
the rate of transpiration. The transpiration of a leaf in still air 
brings into being a layer of moist air around the leaf, and the 
