16 PROTOPLASM AND PLAXT 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 chloroi)lasts, around the pyrenoids will be 

 found masses of starch which become more evident on staining 

 with iodine. 



{(}) 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. 



(/) IMount 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. 



(g) Examine a cross-section of a wlicat grain. The aleuron 

 will be found in a layer of cells outside of the starch-containing 

 cells. This laj^er 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. 



(i) Examine various oily seeds such as cotton, flax, peanut, 

 or an oily fruit such as the avocado (Persea gratissima) or olive. 

 In the cells w^ill 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 



