PARENCHYMA AND ITS MODIFICATIONS. 3 



(c) Make a transverse and a vertical section through the 

 petiole of any water-lily, or through the soft interior of any rush 

 (Juncus). 



(d} When, after considerable practice, the student succeeds 

 in making very thin sections of the foregoing plants, let the 

 reagents for the demonstration of cellulose be applied to them, 

 as directed in 143. 



It is not superfluous to state (1) that success in the application 

 of these and most of the other reagents employed under the 

 microscope is generally preceded by many failures, and (2) that 

 carelessness in the use of some of the reagents may irreparably 

 ruin the microscope lenses. 



Sclerotic Parenchyma. Excellent material can be obtained 

 from the flesh of pears and quinces (see 211 and Fig. 40). 



From the tough shells of many sorts of nuts and seeds (see 

 Fig. 41) good preparations can be made by the method described 

 in 495. For the Canada balsam there recommended good 

 shellac can be advantageously substituted. 



Collenchyma cells are well exhibited by cross-sections of the 

 stem of any common Labiate, for instance Spearmint, or of the 

 stem of almost any of the Umbelliferae (see 216). Apply dilute 

 hydrochloric acid to the sections. 



Wood parenchyma cells are easily obtained by careful macer- 

 ation (70). Dilute solutions of Schulze's liquid are preferable 

 to strong, although much slower in action. Excellent material 

 is afforded by most of the oaks and other hard woods (see 254, 

 255). Nearly all possible intermediate forms can be found by 

 careful search. Apply the tests for "lignin" (154). Use also 

 upon different specimens red and blue coal-tar colors. 



II. EPIDERMAL CELLS. 



(a) Examine a film removed from the upper surface of some 

 fleshy leaf; for instance, Sedum, the cultivated Cotyledon or 

 Eccheveria, Purslane, or Begonia, etc. 



(ft) Compare the cells of this film with those found on the 

 upper surface of a shining petal; e. g., that of Buttercup or 

 Poppy. 



