THE STAMEN 115 



by abortion in early stages, and evidence of the loss may persist in the 

 mature anther. 



Taxonomically, the two-sporangiate, unilocular taxa are commonly 

 considered more advanced tlian the four-sporangiate, bilocular taxa. In 

 the Epacridaceae, the unilocular anthers often show evidence of the 

 fusion of sporangia. The Liliaceae have, typically, four sporangia, but 

 Smilax has only two. Sporangium number is usually constant through- 

 out a genus, but, in Najas and Piper, the stamen is described as having 

 one to four sporangia. Vestiges of the lost sporangia in the form of 

 abortive structures are occasional — Moringaceae, Piperaceae. In highly 

 zygomorphic families with two sporangia, such as the Cannaceae and 

 Marantaceae, the anther may have one lobe normal, with two spo- 

 rangia, and the other lobe petaloid. 



Form of the Sporangium. The sporangium is primitively slender and 

 elongate, as seen in many of the less-advanced famihes of both dicotyle- 

 dons and monocotyledons. In advanced stamens, it has been progres- 

 sively shortened, becoming hemispherical where the anther is globose. 

 Though typically straight, it is frequently crescent-shaped or strongly 

 curved; it may encircle the connective — Vinguicula. Some anther lobes 

 are described as "prolonged." The greater length is perhaps related to 

 increase in amount of pollen in anemophilous taxa. The greater length 

 is prominent in versatile types, because the anther is nearly free from the 

 connective. 



In the laminar stamen, with two pairs of sporangia, the outer member 

 of each pair is somewhat smaller than the inner. This difference in size 

 is more noticeable in specialized anthers where a cross section shows 

 the well-known "butterfly" form; the two smaller sporangia are, in the 

 laminar stamen, those farthest from the midrib. 



Position of Sporangia on the Stamen. In the present century, Httle 

 attention has been given to the fundamental position of the micro- 

 sporangia on the angiosperm sporophyll. The sporangia are usually 

 described as "marginal," a position that, superficially, they seem to 

 have, but it is the pairs of sporangia, not the individual sporangia, that 

 appear marginal. The typical anther is a greatly reduced and specialized 

 part of the primitive, laminar sporophyll and is of little value in deter- 

 mining the basic position of the sporangia. But tlie critical studies of 

 woody ranalian families — Degeneriaceae, Himantandraceae — provide 

 descriptions of undoubtedly primitive stamens and a basis for phylo- 

 genetic comparisons of sporangium distribution on the sporophyll. In 

 these taxa, the sporangia are all on one side, remote from the margin 

 (Fig. 50). Comparisons in many families show that the "marginal" posi- 

 tion was derived by reduction of the lamina, with accompanying "migra- 

 tion" of the sporangia. Evidence that all four sporangia belong on one 



