MATERIAL FOK STUDY OF MULTIPLE EPIDERMIS 51 



coated with a crystalline mass of calcium carbonate. This curious 

 ingrowth of the cell wall, together with its covering of calcium 

 carbonate is termed a cystolith and the cell in which it occurs is 

 known as a lithacyst. (Cf. the recent work of Ajello, 1941.) 

 Ohtain a trans-section of a portion of a living leaf-blade of Ficus 

 elastica and examine it under low and high magnification. The 

 multiple epidermis on the upper (i.e., adaxial) surface consists 

 of several layers of cells the outermost of which are small com- 

 pact and overlaid by a prominent cuticle. These cells thus 

 exhibit the features of a normal "uniseriate epidermis." 



In contrast, the inner eells of the multiple epidermis are rela- 

 tively large and because of their shape, their cellulose walls and 

 the presence of intercellular spaces suggest resemblance to corti- 

 cal parenchyma tissue. Notice that the cells are not aligned in 

 radial rows because, during their formation, both anticlinal as 

 well as periclinal divisions have occurred. A careful inspection 

 of the walls of these cells under high magnification will reveal 

 numerous simple pits. At intervals large sac-like litho>cysts will 

 be seen, protruding into the adjacent palisade parenchyma. 

 These distended cells have arisen directly from the original sur- 

 face cells of the leaf blade. Each lithocyst, unless injured in 

 sectioning the leaf, contains a cystolith with its knob-like end 

 covered by a crystalline mass of calcium carbonate. Introduce 

 a few drops of hydrochloric acid under the cover-glass and 

 observe the rapid dissolution of the calcium carbonate. This is 

 accompanied by the evolution of small bubbles of carbon dioxide. 



V. Trichomes. — This term may be used in a collective sense 

 to designate the diversified types of epidermal appendages such 

 as hairs, scales, colleters and water vesicles. Despite the "end- 

 less" variation in the form and structure of trichomes (cf. 

 De Bary, pp. 54-66, and Netolitzky, 1932), these structures 

 originate from the extension or subdivision of protoderm cells. 

 Trichomes are therefore, morphologically, a part of the epi- 

 dermis in contrast to emergences (e.g., the prickles on the stem 

 of Rosa, Rihes, etc.) which consist of cells derived not only from 

 the protoderm but also from deeper hypodermal layers (cf, 

 De Bary, p. 58, and Eames and MacDaniels, p. 1 and p. 2, Fig. 1). 



