THE STAMEN 



135 



in enlargement, because it is largely responsible for the orientation 

 that determines direction of dehiscence. Increase in cell number on 

 one side of the connective — sometimes by almost cambiumlike growth 

 (Fig. 57) — displaces the sporogenous areas toward the other side — 

 toward the adaxial side where dehiscence is introrse, and toward the 

 abaxial side where dehiscence is extrorse. Latrorse dehiscence develops 

 where a subcylindrical primordium becomes more or less four-sided 

 and tliere is little or no differential growth in die connective. The 



Fig. 58. Cross sections of filament of stamen of Cleome gigantea showing marginal 

 development. I to IV, progressive stages in ontogeny, d, v, dorsal and ventral sides; 

 mi, initials of the meristems; pc, procambium. ( After Kaussmann. ) 



sporogenous areas remain in the corners. The strongly marked differ- 

 ences of orientation in extrorse and introrse anthers are the result of 

 differential growth in the connective — plus, in some taxa, a twisting at 

 the filament tip, as in some palms — and do not indicate an important 

 morphological difference. 



With evolutionary reduction of the sterile tissues of the sporophyll, 

 the protuberance of the sporangial regions increases, but the sporangia 

 remain enclosed by the several-layered anther-sac wall; they do not 

 become "free." The wall layers are progressively reduced, with in- 

 creasing elaboration of the anther lobes, until only two layers remain, 



