198 STUDIES IN FOSSIL BOTANY 



the megasporangium is enclosed in an integument, which 

 in Miadesmia, however, completely roofs in the sporan- 

 gium above, leaving only a narrow opening or micropyle 

 at the distal end (Figs. 83 and 84). The integument is 

 provided with long tentacles, which, as they project 

 beyond the micropyle, may probably have assisted 

 pollination. The sporangial wall is less developed than 

 in Lepidocarpon, the integument having, as it appears, 



Fig. 83. — Miadesmia. jiicmbranacca. Approximately transverse section of seed-like 

 organ. /, /, lamina of sporophyll ; v.b., vascular bundle ; v, velum or integument ; 

 lg, ligule ; sm, sporangium-wall ; m, membrane of megaspore. X about 30. R. S. 

 S. Coll. 2237. 



more completely taken over the function of a protective 

 organ, and no abortive sister-cells of the single megaspore 

 (in which the prothallus is sometimes present) have 

 been observed. Thus the seed-like character is even 

 more striking in Miadesmia than in Lepidocarpon. 

 There seems to be no near affinity between the two 

 genera, which differ widely, especially in the insertion 

 of the sporangium and the position of the micropyle, 

 and in each of which, presumably, the seed-habit was 

 independently evolved. 



