THE ANGIOSPERMAE 



1185 



Biitonius, have sporangia which are symmetrically placed around the con- 

 nective and their dehiscence is neither inwards nor outwards, but lateral. 

 The most general mode of dehiscence is by longitudinal splitting, along 

 the furrow between two paired sporangia. Before this happens the wall 



Fig. 1 1 57. — Flower of Azalea obtiisa with 

 anthers extruding pollen by terminal 

 pores. 



separating the pollen-sacs has itself split or broken down, so that a single 

 line of external dehiscence opens the cavities of both the sporangia of the 

 pair. For this reason there are scarcely ever more than two lines of dehis- 

 cence. Only in the rare cases of multisporangiate anthers {e.g., Viscum) 

 does each sporangium dehisce separately. The line of dehiscence may 

 sometimes be very short and the opening formed is thus no more than a 

 pore, there being also in this case one to each pair of sporangia, except in the 

 Melastomaceae where only one pore 

 serves all four. Porose dehiscence is 

 usually confined to the distal end or only 

 to the apex of the anther {Solarium) but 

 the often quoted case of the " apical " 

 pores in Ericaceae (Fig. 1157) has been 

 shown to be an error. The true apex of 

 the anther in this family is directed in- 

 wards and downwards and the portion 

 in which the pores are formed is really 

 a basal upgrowth. 



Transverse dehiscence also occurs, 

 but it is rare and, except for AlchemiUa, 

 is almost confined to the small family 



B 



Fig. 1158. — Valvate stamens. A, J.aiiiiis. 

 B, Cinnamoimnu. {After Le Maoiit and 

 Decaisne.) 



