64 VEGETABLE HISTOLOGY. 



with the lower surface turned up and cover 

 with a glass. Heat gently till the liquid 

 begins to boil and keep it at that tempera- 

 ture for a few moments, then cool, add 

 another drop of liquid if necessary and ex- 

 amine. 



The leaf has become sufficiently trans- \ K /> 



parent that the epidermal cells, stomata /* ^ ^ 



and hairs can be distinctly observed. The Fig. 41. Epidermis of 

 epidermal cells are polygonal in shape, sto- ^?de d rmai g ecus'- ' 

 mata are present on both surfaces and the guard ceils of a 

 hairs are one-celled with thick, warty walls, SSJWffltfc"" 

 often curved. 



Often the epidermis can be separated by warming a fragment 

 of a leaf in a solution of potassium hydroxide (about 2 per 

 cent.) until it boils, cooling and pressing the cover glass firmly, 

 while at the same time giving it a sliding motion. This method 

 may be tried when chloral hydrate solution fails to clarify uf- 

 ficiently. 



Cross-sections of stomata will be examined in the exercises 

 on stems and leaves. 



CHAPTER XIV. 



EPIDERMAL APPENDAGES. 



All the outgrowths or appendages of the surface of a plant 

 are known as trichomes, which means literally hairs. They 

 consist of one or more cells usually arranged in a row or col- 

 umn, sometimes in a mass. The most common forms of 

 trichomes are 



1. Hairs these are the principal form. 



2. Bristles a single-pointed cell or row of cells, much thick- 

 ened and hardened. 



3. Prickles, like bristles, but stouter. 



4. Scales. 



5. Glands generally short, bearing one or more secreting 

 cells. 



6. Root-hairs, long, thin, single-celled and subterranean. 



7. Sporangia of ferns. 



8. Ovules of flowering plants. 



Trichomes originate mostly from the growth of single epi- 

 dermal cells, and on their first appearance consist of slightly 

 enlarged and protruding cells. These may elongate and form 



