298 FREDERICK A. WOLF 



EXPLANATION OF FIGURES 



1 Diagrammatic representation of a section through one of the diseased areas, 

 showing the way in which cork tissue separates the brown areas from the active 

 tissues below, a, cuticle; b, cork; c, crystal bearing hypoderma; d, collenchyma. 



2 Protrusion of crystal bearing hypodermal cells into the substomatal cavity. 



3 Normal stoma: a, cuticle; b, epidermis; c, hypoderma; d, collenchyma; e, 

 accessory guard cells;/, true guard cells. The dotted line marks the position of 

 the first division of the epidermal cells in barring the stomata. 



4 The formation of cork has resulted in barring the stoma. 



5 Division of the epidermis, the origin of the phellogenetic layer. 



6 Stone cork, four cell layers thick, showing the pores with adjacent thin- 

 walled cork. No pits occur in the secondarily modified wall of the outside cell 

 in the series of stone cork cells. 



7 Layers of stone cork not uniformly thickened. 



8 The beginning of the formation of thick-walled cork at the margin of a dis- 

 eased area. 



9 Two isolated layers of stone cork separated by thin-walled cork. 

 10 A portion of the same as figure 1. 



