THE PRINCIPAL TISSUES. 



71 



(a) Collencliyma may be studied in the stems, petioles, and leaf-ribs 

 of herbaceous Dicotyledons — e.g., in species of Silphium, liheum, 

 Bum'X, Ohenopodium — in many Labiate,, Solanacem, Begoniacece, Ou- 

 curbitacecB, and many others; also in the petioles of the water-lily 

 and young stems of the elder. 



(6) Upon soaking in water, or upon treatment with nitric or sulphu- 

 ric acid, the thickened angles become greatly swollen. 



ft 



Fig. 55.— Longitudmal radial Bection of Btem of Echimcystis hbata. en, epidermis ; 

 CO, conencbyma,; pa, ijarenchyma ; /. a single wood fibre, marked with "crossed'' 

 ^^.e., twisted) pits ; sp, intercellular spaces, x 500. From a drawing by J. C. Arthur. 



(c) Upon treatment with Schultz's Solution the thickened angles are 

 colored light blue. 



(O) Upon slight warming in a solution of potash, and then treating 

 with a solution of iodine in potassium iodide, the thickened angles be- 

 come colored dark blue. 



101.— Solerenehyma. In many plants the hard parts are 

 composed of cells whose walls are thickened, often to a very 



