16 PROTOPLASM AND PLANT CELLS 
(c) Place a dish of water containing Spirogyra in the light 
for some hours and then examine a few filaments. In the 
spirally wound chloroplasts, around the pyrenoids will be 
found masses of starch which become more evident on staining 
with iodine. 
(d) Make thin sections through various leaves that have been 
exposed to the light for some time, staining with iodine. In 
some of these minute grains of starch will be found in the 
chloroplasts. 
(e) Make longitudinal sections of ripened apple twigs, in the 
fall or winter especially, and note the starch stored in the 
rather thick-walled cells of the pith. 
(f) Mount in strong alcohol or glycerine a thin section of a 
pea or bean. In addition to starch grains the cells’ will be 
found to contain very numerous fine granules. Stain with 
iodine. These small aleuron granules will be stained brown 
and the starch blue. To another section apply one of the 
tests for proteins given on p. 9. Mount another section in 
water and note the effect on the aleuron. Examine cotyle- 
dons of germinated peas and beans for presence or absence of 
aleuron: y 
(g) Examine a cross-section of a wheat grain. The aleuron 
will be found in a layer of cells outside of the starch-containing 
cells. This layer is largely removed with the bran in the 
process of making flour. 
(h) Make a thin section of a seed of the castor oil plant 
(Ricinus). Mount without adding water or any other 
reagent. Large aleuron grains will be seen, each containing an 
angular protein crystal and a spherical, so-called ‘‘globoid,”’ of 
inorganic nature. Add a little water and some of the oil will. 
escape and appear at the edges of the section as large drops. 
(t) Examine various oily seeds such as cotton, flax, peanut, 
or an oily fruit such as the avocado (Persea gratissima) or olive. 
In the cells will be found varying amounts of oil. By treating 
the sections with 1 per cent. solution of osmic acid or with 
alkannin solution the oil will be stained respectively black or 
red. 
(j) Make a thin longitudinal section of the stem of spider- 
wort (Tradescantia) and mount in water. Certain thin- 
walled cells will be found containing bundles of needle-shaped 
crystals (raphids). Many of these will be torn out of position 
