50 THE EPIDERMIS 



uiiiseriate epidermis may experience tangential divisions which 

 result in the formation of a uiuUiplc or muUiseriatc epidermis. 

 According to tlie resume of the literature given by Linsbauer 

 (1930, pp. ;58-4;i), the first tangential divisions leading to the 

 development of tiie multiple epidermis occur at a relatively late 

 stage in leaf ontogeny ; in Ficus, for example, as the leaf is 

 expanding and after its stipules have fallen away. Such divi- 

 sions apparently occur first near the middle portions of the 

 lamina and progress towards its margins. Often the tangential 

 divisions are so regular as to produce a tissue composed of thin- 

 walled cells arranged in radial rows. But anticlinal divisions 

 may also occur in the cells thus obscuring the point of origin 

 of the tissue. It should be apparent from these facts that the 

 concept of the "multiple epidermis" is based fundamentally 

 ujion its direct origin from the surface cell layer and not upon 

 its histology or functions. This is important because much con- 

 fusion has been produced, especially in the literature of physio- 

 logical anatomy, by failing to distinguish between a true multiple 

 epidermis and the various types of "hypodermal" tis.sues which 

 originate and develop independently of the epidermis. The chief 

 fimctiem of the multiple epidermis is water storage and a brief 

 discussion of its activities in this direction are summarized by 

 Linsbauer (1930, pp. 41-43). According to the earlier work of 

 l*fitzer which is outlined by Linsbauer, water-storing tissue of 

 epidermal origin may in Peperouiia pereskiaefolia attain a thick- 

 ness of 14-1") layers and thus represents about 7 times the thick- 

 ness of the otiier leaf tissues. 



IV. Material for the Study of the Multiple Epidermis.— A 



typical example of a multiple ei)ldermis is found in the leaf 

 blade of the common "rubber ])lant" {Ficus elastica). As early 

 as 1827, the (Jerman botanist Meyen observed that during the 

 formation of the multiple epidermis in this species, certain of 

 the original epidermal cells fail to divide tangentially but instead 

 become enormously distended inwardly and finally protrude into 

 the underlying palisade parenchyma. During this process of 

 distention, a cui-ious peg-like invagination develops from the 

 outer tangential wall into the cell cavity and eventuallv becomes 



