ILLUSTRATIVE STUDIES 1 97 



which the scarcity of water would be most harmful to the well- 

 being of the plant; and the water-storage tissues keep on dis- 

 tributing their stores untU they themselves are wilted while the 

 tissues to which they are tributory are maintained in a fresh 

 and turgid condition. 



Illustrative Studies 



1. Cut free-hand sections of potato that has lain for some 

 time in 95 per cent, alcohol to harden it. Mount the sections 

 in a drop of water and after studying them with low and high 

 powers let a drop of iodine solution diffuse under the cover- 

 glass. Starch grains will be colored blue to black and pro- 

 teids yellow. The cell-contents can be seen to best advantage 

 around the thinnest edge of the section, but there they will have 

 dropped out to some extent and study of a thicker part of the 

 section may be necessary to find out how densely packed are the 

 cells with reserve food. Draw a few cells with their contents. 

 Measure the starch grains. 



2. Study in a similar manner thin sections of soaked lima 

 bean. Notice how the striations of the starch-grains differ 

 from those of potato starch. Notice the very distinct granules 

 of proteid stained yellow to brownish by the iodine. Draw a 

 few cells with their contents, and measure the grains of reserve 

 food. 



3. Cut with a dry razor free-hand sections of the endosperm 

 of castor bean and transfer them to a watch glass containing 

 95 per cent, alcohol 2 parts and castor oil i part and enough 

 eosin to make a light red solution. After a few hours mount 

 the sections in ricinus oil-alcohol without the eosin. This treat- 

 ment will bring the aleurone grains out clearly and reveal their 

 several parts (page 182); and it will show the grains to be im- 

 bedded in the meshes of the cytoplasm. Draw a few cells to 

 show this, and on a larger scale a single aleurone grain in all its 

 details. 



Put other sections for several hours in alcanna tincture (page 



