CELL-CONTENTS AND FORMS OF CELLS. 259 



cent, in Helianthus annuus to 76.47 per cent, in Dahlia variabilis. 

 It is unaffected by most reagents except hydriodic acid. It may 

 readily be separated in unaltered masses upon treatment of the 

 tissues with Wiesner's chromic acid mixture or with Schultze's 

 macerating solution. Hanausek considers the phytomelane layer to 

 be in the nature of a mechanical protection to those fruits and seeds 

 in which the epidermal and hypodermal layers scale off with the 

 ripening of the fruit. (Consult Kraemer and Sollenberger, Amer. 



I II 



FIG. 130. Striation in cell-wall: I, a portion of bast fiber in Oleander, showing left 

 spiral bands as seen from the outer surface (a) and the same as seen from the inner surface 

 (b); II, portion of the bast cell of Asdepias syriaca as seen on the under surface; III, a 

 view of the bast fiber of Asdepias syriaca as seen when looking through the middle of the 

 cell; IV, portion of tracheid of Pinus sylvestris, showing two views of the striations of the 

 wall. After Dippel in "Das Mikroskop." 



Jour. Pharni., 1911, p. 315; Senft, PJiarm. Post, 1914, No. 30: 

 Hanausek, Ber. d. d. bot. Ges., 1911, p. 558.) 



LAMELLAE. In some cells, as in lignified cells, the lamellae 

 are quite apparent. In other cases the use of reagents, as chromic 

 acid or chlor-zinc iodide, is necessary to bring out this structure. 

 The layering which is observed in transverse sections of the cell- 

 wall is spoken of as stratification of the wall (Fig. 129), whereas 

 the layering observed in longitudinal or tangential sections is 

 referred to as striation of the wall (Fig. 130). 



