66 



VEGETABLE HISTOLOGY. 



in alcannin solution and note the 

 effect upon the resinous matter. 



The other two kinds of gland-hairs 

 are very short. One has an oblong 

 gland while the gland cell of the 

 other is round. Note the number of 

 cells in the stalk of each. The cells 

 are very short. 



Note which of the three kinds is 

 most abundant. 



Submit a section to the action of 

 chlor-zinc-iodine solution for about 

 half an hour and then examine. The 

 outer layer of the walls of the hair- 

 cells is stained brown, showing 

 cutinization ; the inner portion of the 

 walls may be blue, showing cellulose 

 substance. 



Try the clearing effect of chloral- 

 hydrate solution on the gland-hairs. 

 The contents will gradually disappear, leaving the cell-wall dis- 

 tinct, and the gland-cell structure may now be studied. 



It is thought that the purpose of hairs and glands is to afford 

 protection to the plant against insects, etc. The odor of the 

 Geranium is due to the secretions of the gland-hairs. 



Fig. 42. Hairs on Geranium 

 stem. 1, simple hair ; 2, 3, 4, 

 three forms of gland hairs 

 (reduced, from Bastin). 



HAIRS ON OTHER PLANTS. 



For variety, let the hairs on the following plants be studied : 



Clamp a piece of Mullein leaf between pith and cut several 



sections. Mount them in water and examine. A dense growth 



of branched hairs covers the leaf and beneath these, close to 



the surface, will be found a few short glandular hairs. 



Clamp a moderately large vein (with a portion of the leaf on 

 each side) of Stramonium, Digitalis, Belladonna and Hyos- 

 cyamus leaf respectively in pith and cut cross-sections. Exam- 

 ine these in water or chloral hydrate solution. Compare the 

 hairs and make drawings. These are leaves of four important 

 official drugs and the comparison of the hairs should therefore 

 be of special interest. 



