MORPHOLOGY OF HIGHER PLANTS. 



177 



P). Cell-membrane Mucilage, a. Secondary thickening of 

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

 of Rhamnus Frangnla; bark of root of Sassafras officinale; 

 inner bark of Ulmns fulva; leaves of Barosma hctulina, and B. 

 crcnulata; seed-coat of Cydonia vulgaris; seed-coat of Linuni usi- 

 fatissiniiiin: seed-coat of Sinapis alba, and Brassica nigra, 

 b. ^Metamorphosis of Cell wall : i. Pith and mediillary-rav 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 

 T",-ith 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. 



acege. 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 Jlola 

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

 Prnnns ax'iuin. 



The origin of mucilage may be satisfactorily studied in the 

 fresh tuber of salep and in the root of alth?ea in the former as 

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



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