361 



MESSES. CTEIL WEST AND H. TAKEDA ON 



The individual cells of the marginal region exhibit unequal growth, as a result of which 

 they become very loosely attached to one another, and ultimately produce narrow, 

 irregular lobes (PL 36. fig. 34). 



The cells of the thicker central region of the ligule form a very loose tissue, and 



enclose large 



intercellular spaces 



(PI. 36. figs. 



30-32). Even the epidermal cells 



are not compact; they are always covered with a very thin, but nevertheless quite 

 distinct cuticle, which does not follow the outline of the cells, but leaves small inter- 

 cellular spaces between them, thereby producing an effect which recalls that produced 

 in the leaves of a plum-tree when attacked by the 'silver-leaf' fungus {=8tereum 



purpureum). 



The cells of the lamina of the ligule have dense protoplasmic contents ; these cells 



secrete mucilage (PI. 36. 



figs. 



29-31). The secretion 



of mucilage by the ligule has 



Text-fig. 19. 



Isoetes lactistrls. Transverse section through base of leaf-rosette. The ligules are darkly shaded, x 20. 



previously been described for I. lacustris by Farmer (14, p. 44), and for I. Systrix by 

 Scott and Hill (28, p. 442). 



The cells of the glossopodium are very large, and contain relatively little protoplasm ; 

 but in I. japonica a band of large empty cells, such as Wilson Smith describes and 

 figures for I. echinospora (30, p. 233, PI. 14, g in fig. 22), was never observed. 



The glossopodium is surrounded by a sheath of more or less isodiametric cells, the 

 central portion of the radial walls of which appears to be lignified (PL 36. fig. 42). This 

 structure, which closely resembles an endodermis, has already been described and figured 

 by Bruchmann (7, p. 576, Taf. 24. figs. 22-25). 



Certain cells of the leaf -base outside the glossopodium become converted into short 

 reticulate tracheids. These elements, which are invariably found in close proximity to 



