36 A LABORATORY MANUAL OF BOTANY 
may frequently be determined by observation of the un- 
stained specimen, but may be demonstrated by the addition 
of a weak solution of iodine. This causes the starch grains 
to assume a bright-blue, deep-blue, or brownish-blue eolor. 
Make thin sections of the storage tissues at hand, stain 
them with iodine, and examine them under low power of 
the microscope. Sketch all specimens studied, showing the 
following points: 
How much of the structure is used as a storage organ? 
Has the storage tissue a protective covering? If present, 
against what do you think it protects? What is the form of 
the storage cells? Are all equally filled with stored food? 
Are all starch grains of similar size and form? What 
plants studied have most stored food relative to the amount 
of storage structures used? Which have actually the larg- 
est amount? 
In your notes describe the form and position of each 
storage structure with reference to the plant observed. De- 
scribe also the form, arrangement, and storage capacity of 
the storage tissues in each. 
LESSON XIX 
Field study of storage of foods 
Materials.—Those of the last lesson with others that 
may be located in the field. The most favorable time for 
this work is in early autumn or early spring, when such 
plants as bitter cress, violets, dog-tooth violet, bloodroot, 
hepatica, mullein, sour dock, spring-beauty, etc., and leaves 
of other deciduous plants are to be found. 
Observation and study.—By means of a trowel or sharp 
stick carefully dig down to the storage region of such plants 
as the spring-beauty or Dutchman’s-breeches. Note its 
depth from the surface of the soil. Is this about the same 
with different specimens of a given species? Is it the same 
