62 THE ELEMENTS OF VEGETABLE HISTOLOGY 



Sugars. The chief sugars found in plants are 

 glucose, levulose and sucrose (cane sugar). The 

 empirical formula for glucose and levulose is CeH^Oe, 

 while that of sucrose is C^H^On. The sugars occur 

 in solution in the living plant tissues and like inulin, 

 they may be precipitated by the addition of alcohol. 

 The general reactions for the identification of sugars 

 in plant cells are as follows: 



1. Addition of alpha-naphtho! solution, followed by a few drops 



of concentrated sulphuric acid, yields a violet coloration. 

 Inulin also responds to this test. 



2. Treat the material with copper sulphate solution (20 per 



cent), wash, add alkaline Rochelle salt solution (potas- 

 sium hydroxide 10 gms., Rochelle salt 10 gms., in 100 

 mils of water) and boil. Cuprous oxide will be pre- 

 cipitated in cells containing sugars and will appear black 

 by transmitted light and red by dark field illumination. 



3. Many sugars form characteristic crystalline osazones upon 



treatment with phenylhydrazine in the presence of acetic 

 acid. The sections should be boiled for at least one hour 

 with the phenylhydrazine solution and then rapidly 

 cooled. Unless thick sections are employed the sugars 

 will be dissolved in the reagent and the precipitate will 

 form at the bottom of the liquid rather than in the individ- 

 ual cells. The phenylhydrazine solution is prepared 

 according to the formula noted in the Appendix. 



Alkaloids. Alkaloids are basic compounds con- 

 taining carbon, hydrogen, nitrogen and oxygen, 

 although the latter element is wanting in the liquid 

 alkaloids. Their toxic effects upon animals and plants 

 are of great interest, and the salts of these alkaloids 

 are among the most important items in our materia 

 medica. The alkaloids, being basic in reaction, readily 

 form salts with the acids present in the plant cells, 

 and these alkaloidal salts present in the plant are 

 usually in solution. The microchemical reactions of 



