THE MICROSPORANGIUM 



29 



It is reasonably assured, therefore, that cauline micro- 

 sporangia occu^ 1 in at least seven genera, both Monocotyledons 

 and Dicotyledons being represented. Upon the whole, they 

 seem more characteristic of the primitive members of these 

 two groups than of the more highly specialized members, but 

 this impression may disappear with further investigation. If 

 the cauline origin of megasporangia be considered, the primi- 

 tive character of this feature becomes increasingly uncertain, 

 for cauline megasporangia are common even in the highest 

 groups. It seems probable, therefore, that the cauline or foliar 

 origin of sporangia among Angiosperms is not to be taken as 

 an argument for or against the primitive character of the group 

 in which they occur. The particular organ developing micro- 

 sporangia was probably determined not by its morphological 

 nature, but by what may be called its physiological relations 

 (Fig. 6). Even among Pteridophytes, the sporangia of Lycopo- 

 dium are foliar, and those of the nearly allied Selaginella cau- 

 line; and among Gymnosperms sporangia have both origins. 

 It is evident, therefore, that the distinguishing morphological 



FIG. 7. Lilium philadelphicum. Transverse section of almost mature anther ; nearly 

 all the walls separating the microsporangia have broken down ; highly developed 

 stomium (*) and endothecium (with its rib-like thickenings) very prominent; x 25. 

 From a drawing by W. J. G. LAND. 



structure is the sporangium rather than any member of the 

 plant body from which it may arise. 



In most cases the stamen produces four microsporangia 

 (Fig. 7), and the exceptions noted thus far are by n'o means 



