THE ROOT 163 
flowers, fruit and seed in a single season, then die. Examples: 
Stramonium, Lobelia, etc. 
2. Biennial plants develop but one set of aerial organs the 
first year, e.g., the leaves, and, as Digitalis, Conium, etc., a large 
amount of reserve food material is stored in the roots for the 
Nd 
ed 
2 
poms 
Fic. 97.—Photomicrograph of a transverse section of the stem of a dicot- 
yledonous host-plant infested with the parasite, Dodder. Note the haustoria extend- 
ing from the Dodder (D, D’) into the cortex of the host (H). Greatly enlarged. 
(Gager.) 
support of the plant the following season, when it flowers, fruits 
and dies. 
3. Perennial plants are those whose roots or underground stems 
and roots live indefinitely, as trees, shrubs and perennial herbs. 
Root Hisrotocy.—The histology of roots varies, depending 
upon character of the surrounding water relations or soil in which 
