48 STRUCTURE AXD PHYSIOLOGY OF SEED PLANTS 



section from the interior of the bulb, examine with a mod- 

 erate power of the microscope, and note the thin-walled cells 

 of which it is composed. 



C. Split another onion from top to bottom and try to find : 



1. The broad flattened stem inside at the base. 



2. The central bud. 



3. The bulb scales. 



4. In some onions (particularly in large, irregular ones) the 

 bulblets, or side bulbs, arising in the axes of the scales 



near the base. 



D. Test the cut surfaces for starch. 



EXPERIMENT XXV 



Testing for reserve sugar in an onion. Boil some slices of onion in a little 

 water and filter the latter through a paper filter to remove bits of the bulb 

 that may be left in it. Add a little Fehling's solution to the liquid thus 

 obtained and heat to boiling. Result ? i What is proved ? 



EXPERIMENT XXVI 



Testing an onion for proteids. Heat a rather thick slice of onion in a por- 

 celain evaporating dish v^ith a little strong nitric acid until the latter just 

 begins to boil. 2 Pour off the excess of acid, rinse the portion of onion for 

 a moment with water, and add enough ammonia to cover it. Note any 

 color changes. What is proved ? 



BUDS 



35. Dissection of the horse-chestnut bud.^ * * Examine one of 



the lateral buds on a twig in its winter or early spring condition. 



A. Make a sketch of the external appearance of the bud as 



seen with a lens. How are the scales arranged ? Notice the 



sticky coating upon them. 



1 The mixture usually blackens at length, probably owing to the presence of 

 sulphur in the onion. 



2 Do not allow the acid to touch the hands or the clothing. 



3 Buds of buckeye, maple, or box elder will answer, but not as well. They may 

 be forced to open early by placing twigs in water in a warm room lor several weeks. 



