THE STEM 115 
organs in response to sunlight. Stems and leaves, however, re- 
spond to artificial light as well as to sunlight, so that it is better 
to use the general term, phototropism, than the specific one, 
heliotropism. 
Etiolation. Stems that grow in the dark have a tendency to 
grow longer and to be more slender than those that develop in the 
light. They also have a blanched appearance, due to a lack of 

_ Fig.112. Etiolated seedlings (left) and normal seedlings (right) of mungo 
bean (Phaseolus radiatus) 
chlorophyll. The leaves of plants grown in the dark are usually 
small and also have a blanched appearance. Plants that have 
stems and leaves with these characteristics, which are the result 
of growth in the dark, are said to be etiolated. Etiolation is 
well illustrated in Fig. 112. A practical use is made of etiola- 
tion in China and Japan, where young sprouts of bamboo are 
used for food. These are made white and tender by cover- 
ing them with earth or earthenware jars. Similar results are 
achieved with asparagus by cutting the shoots when the tops 
are just aboveground. 
a 
