6 5 8 
Campbell . — The Structure and Affinities of 
is a mass of irregular isodiametric cells, and no evidence of a procambium 
cylinder, the elongated cells lower down being assignable to the leaf-traces. 
C 
Text-fig. 2. A, b, Two nearly median sections of a young sporophyte in which the second 
leaf, Z 2 , was well advanced ; the stem-apex, st . , and second root, r 2 , are shown in A. h, tannin 
hairs, x about 35. c, Stem-apex, more highly magnified. 
The Cotyledon. 
As has already been indicated, the form of the cotyledon is somewhat 
variable. The petiole is more or less strongly winged, but no stipules are 
developed. Text-fig. 3, A, shows a section of the petiole. The conspicuous 
vascular bundle is elongated in cross-section and is concentric in structure, 
the phloem being of nearly equal width all round, although somewhat less 
developed on the ventral side. No definite endodermis can be recognized. 
No mucilage ducts are present, but there are a number of tannin cells, 
filled with opaque dark contents. These form an irregular ring about the 
vascular bundle. 
The epidermis is much alike on the two sides of the leaf, except that 
stomata are developed only upon the lower surface. The mesophyll does 
not show any development of palisade cells, but is composed of about 
half a dozen layers of nearly uniform cells with irregular intercellular spaces, 
