MORPHOLOGY OF HIGHER PLANTS. 



177 



B. Cell-membrane Mucilage, a. Secondary thickening of 

 wall : Root of Althaa officinalis; bark of Cinnamomum sp. ; bark 

 of Rhamnus Frangula; bark of root of Sassafras oMcinale; 

 inner bark of Ultntis ftilva; leaves of Barosma hetulina, and B. 

 creniilata; seed-coat of Cydonia vulgaris; seed-coat of Linum nsi- 

 tatissimum ; seed-coat of Sinapis alba, and Brassica nigra. 

 b. Metamorphosis of Cell wall : i. Pith and medullary-ray cells; 

 Astragalus sp., yielding tragacanth. 2. Parenchyma cells of 

 ■wood and bark ; cherry gum, yielded by some of the Amygdal- 



FiG. 100. A, B, C, successive stages in the development of the mucilage hairs or glands 

 on the lobes of the leaves of Viola tricolor: D, young secretion hair showing some of the cells 

 with large nuclei and several vacuoles: E, mature hair; F, gland showing mucilaginous layer 

 beneath the cutin and the protrusion of a portion of the mucilage through the broken wall. 



acese. 3. Various cells of the bark; Acacia Senegal, yielding gum 

 arabic. 4. Primary wall as intercellular substance; thallus of 

 Chondrus crispus (Irish moss). (See Figs. 99, 100, 274.) 



C. Glandular Hairs (Driizenzotten) : Leaf and calyx of Viola 

 tricolor (Fig. 100) and leaves of Coffea arabica (coffee) and of 

 Prunus asvium. 



The origin of mucilage may be satisfactorily studied in the 

 fresh tuber of salep and iii the root of althsea^in the former as 

 a cell-content mucilage, and in the latter as a cell-wall mucilage. 



