254 CEREAL GRAINS AND STARCHY TUBERS. 



coat of gluten cells insoluble in water, resists softening for a long 

 time. Embedding may be done in any convenient manner, as the 

 sections are easily cut when the grain is slightly softened. Per- 

 haps paraffin is the best material for the purpose, as it holds the 

 grain so firmly that it may be cut in any direction. No elaborate 

 microtome is necessary. Any simple section-cutting contrivance 

 answers quite well. But care must be taken to have the knife as 

 sharp as possible. The requisite thickness, or rather thinness, of 

 sections is a matter of some importance. The starch-grains will 

 all fall out if the sections are too thin, and the gluten cells will be 

 disagreeably opaque if they are too thick. But as a great number 

 of sections can be cut from a single grain, a selection can easily 

 be made of such as appear of a proper degree of transparency. 



Glycerine jelly is the best medium for mounting. This must 

 be softened to the requisite degree of fluidity by placing it in a cup 

 of warm water. The sections are best removed from the knife by 

 a camel's-hair pencil. If they are deposited in a shallow dish of 

 water, they may be taken up with the pencil as wanted and placed 

 upon the slide, the centre of which should be marked on the back 

 with a dot of ink. If the slide is held inclined, a drop of water 

 placed above the section will run down and carry away nearly all 

 the surrounding grains of starch. If any starch-grains remain, 

 they may be removed with a small brush. Now, while holding the 

 slide in a horizontal position, take a cover in the forceps, warm it 

 slightly over a spirit-lamp, and holding its exact centre over the 

 section, lower it carefully upon the gelatine. If this is carefully 

 done, the cover will settle down to its place without disturbing the 

 starch-cells. Any attempt to move the cover or to press it down 

 will cause a cloud of starch to issue from the cells. Should the 

 gelatine become somewhat hardened before the cover is put on, so 

 that it does not go down of its own weight, allow the gelatine to 

 become quite hard, then place a slight weight on the cover and 

 gently warm the slide over a lamp. The cover then will settle 

 down to its place without disturbing the starch. 



The most difficult sections to mount are those of oats and 

 wheat, while little difficulty will be experienced with Indian corn, 

 barley, or rye. Sections of potato and other starchy tubers are 

 easily mounted by following the foregoing directions. All attempts 



