1 90 



MARSILEACEAE 



[CH. 



Fig. 471. A, B, C. ScAizaea riepesirzs, sections of young (eitile leaves. ^, transverse section of the 

 rachis and longitudinal of the bases of two pinnae, the xylem indicating the adaxial face. ( x 85.) 

 B, longitudinal section of a young pinna, showing the slightly acropetal succession of the 

 sporangia. ( x 85.) C, transverse section through a number of pinnae, showing their relation to one 

 another. (X35.) 



Lateral fusion of such pinnae would give a body similar to that postulated, 

 dut orientated on the opposite side of the leaf, i.e., abaxially. If, however, two 

 similar series of pinnules were flexed adaxially instead of abaxially, with 

 the same alternation, and the same marginal origin of the sporangia, but 

 inclined now to the upper (adaxial) surface, and fused laterally, they would 

 give the structure of the Marsilea sporocarp. (Compare Fig. 466, //^.) The 

 hypothesis entertained is that this is the nature of that body, consolidated 

 by indusial tissue, which surrounds and embeds the adaxially-directed 

 sporangia. But before it can be considered as demonstrated a critical re- 

 examination of the details of development will be necessary, and especially 

 of the vascular tracts. 



(8) The sporangial segmentation is of the Schizaeaceous type, but the 

 adult features are chiefly negative, though Campbell recognises in the 

 abortive annulus and oblique form a similarity to Schizaea. 



