29] 



CHAPTER II. THE TISSUES. 



103 



plerome, and periblein. But there is this distinctive peculiarity 

 about the dermatogen of the root, that its cells undergo division, 

 not anticlinally only, as in the stem, but periclinally also, so that 

 the epidermis of the root is many-layered (except in Hydrocharis 



FIG. 81. Median longitudinal section through the growing-point of the root of Hbrdettm 

 vulgare (Barley) : r root- cap ; fc initial cells of the dermatogen of the many-layered epider- 

 mis; d-<m cortex; d epiblem with mucilaginous external layer of cell-wall c ; t cortical 

 tissue with intercellular spaces; en endodermis ; the whole periblem (pr) is derived from 

 the single layer of two initial cells at the apex ; pi plerome ;.a row of cells which give rise 

 to a large central wood-vessel. (After Strasburger : x 180.) 



and Lemna, where it remains a single layer). This many-layered 

 epidermis, however, is gradually exfoliated as the parts grow 



