18 STRUCTURE AND LIFE-HISTORY OF HAY-SCENTED FERN. 



In the mature internode (figs. 63, 64, 67, 97) we find externally an 

 irregular black, sclerosed epidermis (see table of measurements p. 19). 

 The inner walls often bear rod-like thickenings projecting- into the lumen 

 of the underlying- cells (figf. 63). Next within comes a broad zone of black- 

 walled sclerotic cortex, ten to twelve cells deep. These cells (fig. 63, s) 

 are ang-ular and do not inclose intercellular spaces. Although mostly 

 appearing empty, they may contain considerable amounts of starch, espe- 

 cially in the inner members. They are largest in the middle of the zone. 

 There are pores of different sizes and shapes irregularly scattered over the 

 walls. The ends of the cells are oblique or bluntly tapering (fig. 64; see 

 table, p. 19). 



Sharply demarcated from the sclerotic cortex by a sudden change in the 

 character of the wall is a narrow layer of starchy cortex (figs. 63, 64, st.), 

 This layer is from three to eight cells thick. The cell-walls are thin and 

 colorless. They inclose protoplasm and nucleus, and are densely packed 

 with starch. Intercellular spaces are easily perceptible here between the 

 rounded cells. The end walls are transverse or are slightly oblique (see 

 table, p. 19). 



The cortex is bounded on its inner side by a continuous sheath of endo- 

 dermis a circle, in cross-section, of flattened but irregular cells, very poor 

 in contents (figs. 63, 64, 67, 97). Each radial wall bears a thickened band 

 which stains with safranin (see table, p. 19). 



Within this layer intercellular spaces can be no longer found, but we 

 encounter a thick ring of vascular tissue, which again incloses a rod-like 

 core of starchy and sclerotic cells (medulla). In short, the vascular sys- 

 tem constitutes a cylindrical tube. The vascular ring itself shows, passing, 

 from without inward, successive rings of 



(1) Endodermis. (7) Inner conjunctive parenchyma. 



(2) Pericycle. (8) Inner phloem. 



(3) Protophloem. (9) Inner protophloem. 



(4) Phloem. (10) Inner pericycle. 



(5) Conjunctive parenchyma. (u) Inner endodermis. 



(6) Xylem. 



In the words of Gwynne-Vaughan (1903): 



The xylem ring is surrounded both externally and internally by a complete ring of 

 phloem and pericycle, and the whole is delimited from the ground tissue on both sides 

 by a well-marked endodermis. 



The outer pericycle (fig. 63) consists of two or three layers of angular 

 cells, densely packed with starch. Their walls tend to lie in radial and 

 tangential planes, and the radial walls are often in continuity with those 

 of the endodermis (see table, p. 19). 



Protophloem is difficultly discernible in the old stem, though it forms an 

 almost continuous ring of cells. The elements are greatly elongated, very 

 slender, angular, of various shapes and sizes, with finely tapering ends. 



