CELL-CONTENTS AND FORMS OF CELLS. 219 



alcoholic solutions of Congo red, methylene blue, etc., which dis- 

 tinctly color the mucilage in them. Cell-content mucilages are also 

 found in the fleshy scales of the onion, the rhizome of Agropyron 

 repens, the fleshy leaves of -Aloe and other succulent plants. It 



ms 



mst 



Fig. 118. Cross section through pith (m) and the inner portion of the wood (lb) of 

 Astragalus gummifer, showing successive stages in the modification of the walls in the 

 formation of gum tragacanth (o, i, 2, 3, 4). Some of the tracheae (c) contain globular 

 masses of gum. — After Tschirch. 



probably also occurs in this form in the Cyanophyceae and in 

 some of the red algae, as Laminaria, although in the latter it is 

 formed chiefly as a modification of a cell-wall and the intercellular 

 substance. In Dicotyledons the mucilage which is present is 



