52 HOW TO USE THE MICROSCOPE 



stained than the protoplasm, and if we look exceed- 

 ingly carefully, it is highly probable that we shall 

 discover within the nucleus a minute, deepl}^ stained, 

 granular body, called the "nucleolus." Reference 

 to a botanical treatise will enable us to appreciate 

 the functions of these two bodies, and the wonders 

 we are able to see. 



The iodine solution is not only a stain, it is also a 

 reagent, and the serious worker will find many uses 

 for it. It is very commonly used to demonstrate 

 the presence or absence of starch. If starch is 

 present iodine will stain it blue. A potato is packed 

 with starch grains, which make interesting objects. 

 If a potato be cut, and its freshly cut surface be 

 scraped with a knife, a very small quantity of the 

 scrapings will yield abundance of starch grains for 

 microscopic purposes. Mount some of the scrapings 

 in water, and treat with iodine in manner already 

 described in regard to hairs of Primula. The 

 grains will be stained blue. 



But to make an even more satisfactory examina- 

 tion, a very thin section sliced from a potato with a 

 razor (which should be moistened with water) should 

 be mounted and examined with a J-inch or ^-inch 

 power. The grains can thus be seen packed in their 

 cells, and protoplasm, very small in quantity, wiU 

 also appear. The grains of potato starch are some- 

 what oval, and are bright in appearance. At or 

 near one end of each grain there is a spot known as 

 the "hilum," and each grain is built up in several 

 layers or stratifications. 



It is interesting to compare various kinds of 

 starch grains, and the ability to distinguish the 



