CELL-CONTENTS AND FORMS OF CELLS. 221 



result of a metamorphosis of the cell-wall, is of frequent occur- 

 rence, being found in all parts of the plant, including the endo- 

 sperm cells of seeds, parenchyma cells and medullary ray cells of 

 roots and stems, and epidermal cells of leaves, stems, fruits, and 

 seeds. Cell-membrane mucilage is also found in some of the 

 mucilaginous marine algae, as chondrus laminaria, etc., although 

 in the latter case the mucilage is often spoken of as being derived 

 from the intercellular substance, being a modification of the 



FIG. 1 20. 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; 

 G, portion of leaf on the upper part of the lobes of which occur the mucilage gla'nds. 



primary wall. It may also occur as a result of a decomposition of 

 the secondary lamellae. 



Four different forms of mucilage are recognized, i. Mucilage 

 cells, or distinct cells resembling more or less the surrounding 

 cells, except that they contain mucilage, occur in the tissues of 

 leaves, petals, fruits, seeds, and the parenchyma cells of pith 

 and primary cortex of a number of plants. In this group may also 

 be included the gelatinized cells of the integumental tissues 



