THE STAMEN 127 



around the sporogenous cells persist and, where the protuberances are 

 large and unusually thick-walled, are perhaps added to from nearby 

 regions. The anther-sac wall, thus formed, is laminar in nature, not a 

 true sporangium wall. The entire anther-sac wall or one or more layers 

 of it have frequently been described as the sporangium wall, but the 

 stamens of the Ranales show clearly the naked character of the sporo- 

 genous tissue. The protruding sporangia, though histologically and 

 functionally walled, are "morphologically naked"; even in the most 

 thin-walled and free anther lobes, the sporangium is "sunken." In anther 

 sacs, the sporangia are in a position more favorable for pollen distribu- 

 tion than in the center of a laminar stamen. (The megasporangium is 

 probably also naked, though in interpretation of the morphology of the 

 ovule, the nucellus is commonly considered the sporangium wall.) 



The importance of the wall-less character of the angiosperm micro- 

 sporangium seems to have been neglected. The apparent presence of a 

 sporangium wall — the anther-sac wall and the endothecium — has ob- 

 scured the wall-less condition. Absence of a sporangium wall is prob- 

 ably an important angiosperm character, one that will play a major 

 part in the determination of the ancestry of the angiosperms. 



The Pollen-containing Chamber. Several terms have been applied to 

 the pollen-containing chamber: anther chamber, pollen sac, locule, 

 theca. Anther lobe, anther sac, and anther half, though obviously cover- 

 ing more than the chamber and its contents, have sometimes been used 

 as synonyms. All these are morphologically loose terms, because they 

 may represent one, two, or four sporangia. The term theca is perhaps 

 the most used and has unfortunately come to be well established, sup- 

 planting others because it is less technical. Pollen chamber is an un- 

 desirable term, because it may suggest the entirely different pollen- 

 receiving chamber of the gymnosperms. All these terms must remain 

 loose, general terms, but theca should be avoided in technical descrip- 

 tions because it may represent one, two, or, rarely, more sporangia. It 

 was called obsolete in morphological literature many years ago. 



Anthers with two lobes are termed dithecoiis; with one lobe, mono- 

 thecotis. (Both these terms are morphologically unsatisfactory, because 

 they involve the loose term theca.) The dithecous anther is a typical 

 complete anther with four sporangia; the monothecous anther is usu- 

 ally a half-anther with two sporangia, the sporangia of a lateral half of 

 a typical anther. But the monothecous anther may have the sporangia 

 of one lateral half abortive or absent, as in many Labiatae; it is rarely 

 a transverse half of an anther, with one sporangium of each lobe abor- 

 tive. An anther described as monothecous may have one, two, or four 

 sporangia, with their contents united in a common chamber. The anther 

 sac usually contains the pollen of two sporangia, but, in latrorse 



