136 



MORPHOLOGY OF THE ANGIOSPERMS 



an epidermis and one hypodermal layer (Fig. 59). "Uniseriate" anther 

 walls — so-called "sporangium walls" — are probably misinterpretations 

 of biseriate walls where the epidermis has been lost ontogenetically 

 (Fig. 59C, G, H). Even in aquatic plants with extreme tissue reduction 



Fig. 59. Cross sections of anther-lobe walls showing reduction at maturity to epi- 

 dermis and one hypodermal layer in A, D, I, or to the hypodermal layer with 

 fragments of epidermis persisting in the other diagrams. E, swollen cells over septum 

 which ruptures the wall at dehiscence. A, Humulus; B, Broussonetia; C, Dorstenia; 

 D, E, Zannichellia; F, Trema; G, Casuarina; H, Ricinus; I, Zostera. {After 

 Staedtler. ) 



throughout the flower, the anther wall is two-layered. In the angio- 

 sperms, there is no sporangium wall distinct from enclosing tissues of 

 the sporophyll. The description of the microsporangium wall as "many 

 layered" is based on the interpretation of tlie anther-sac wall as the 

 sporangium wall. 



The filament commonly remains very short — sometimes a mere base 

 for the developing anther — until late stages in flower development. Its 



