G. R. Wieland — American Fossil Cycads. 431 



well defined layer of small elongate cells, a single cell in thick- 

 ness, or several cells in thickness between the angles formed 

 by adjacent sporangia, and thus covering the entire inner face 

 of the synangium, as early cleft down to the sporangial bases. 

 (See figure 3.) 



Along the inner middle surface of each sporangium this 

 tissue weakens to form a well marked dehiscent line, along 

 which splitting is frequently seen to have taken place in unex- 

 panded stages of frond growth, though 

 such premature dehiscence is probably 3 



due to the process of silicification. 



Recapitulating, then, the principal fea- 

 tures of the synangium are : First, the 

 outer palisaded wall tissue ; second, the 

 delicate thin-walled layer usually collaps- 

 ing or failing of well marked preservation ; 

 third, the sporangial loculi containing 

 much well-preserved pollen but delimited 

 only by dessicated pollen grains or col- 

 lapsed remains of cells ; and fourth, the 

 thin elongate-celled layer bounding the 

 sulcus between the two rows of sporan- 

 gia : — dehiscence of the synangium taking 

 place early along the median apical line, 

 and of the sporangium, longitudinally 

 along the inner median line, as in the 

 genus Marattia, not Dance. 



Regarding the character of the tissue 

 bounding the sporangial loculi a word 

 remains to be said. The yellowish-brown 

 iron-stained band, mentioned above 



is 



Figure 3. — Cycadeoidea 

 dacotensis Macbride. Lon- 



more distinct in the less advanced stages gitudinai transverse sec- 

 observed thus ^ far, but in all cases the sWinT^ttachmTn^To 

 collapsed remains of cells composing it so the sporophyii, the sev- 

 uniformly lack structure that it has not eral la y ers of the s ? nan - 



, ^ •! i j. j . • ,i , gial wall, its dehiscence, 



yet proven possible to determine the true f he atta ' chment of th e 



Character of the locular wall, as to whether sporangia, and the median 



wholly septal, or in part tapetal. It sulcus or fissure between 

 would appear however that it may have ^Z^on^Zlll 

 been two cells in thickness, rather than is characteristic. x37. 

 one, in this respect approaching the con- 

 dition of the crushed double layer of wall cells observed by 

 Lang in Stangeria paradoxa. See Lang, Studies in the 

 Development and Morphology of Cycadean Sporangia, Plate 

 XXII, figures 15 and 16. If by any chance the colored band 

 represents a long persistent but finally crushed tapetum, the 

 condition represented would be quite identical layer by layer 



