ORGANIZATION OF VOLKMANNIA DAWSONI. 33 



the prosenchymatous cells composing the bractigerous 

 disk and the lower portions of the bracts is shown in 



fig- 7- 



The Sporangia. — These are arranged, nearly in a single 



plane, in the concavo-convex space between each two con- 

 tiguous bractigerous disks, and appear to be grouped in 

 from three to four irregular concentric circles within each 

 space. Each sporangium has a mean diameter of about 

 •06. The sporangium-wall (g) is dense, thick, and cellular ; 

 but defective mineralization prevents my ascertaining the 

 exact arrangement of its cells. I have already pointed 

 out that the sporangiophores are so numerous as to suggest 

 the probability that there is a separate one for each spor- 

 angium. They arise entirely from the bractigerous disk, 

 and not from the bracts. In fig. 2 we have, at h, a tangential 

 section crossing one of these disks ; and its upper surface 

 is seen to be crenulated with the intersected bases of these 

 sporangiophores. They are also seen in great numbers, 

 sometimes intersected longitudinally, but more frequently 

 transversely, at h h in the sections 3 and 4. Their mean 

 diameter is about '0075. Fig. 7 represents the base of one 

 of these sporangiophores, seen near the base of the lower 

 right-hand bract of fig. if" , but more highly magnified; and 

 fig. 8 exhibits atrausverse section of one of them still more 

 enlarged. Both these sections demonstrate their cellular 

 character. They may possibly have contained a few vessels ; 

 but I have not succeeded in detecting them. Since these 

 organs all spring from the bractigerous disks, those sus- 

 taining the outermost series of sporangia must have re- 

 quired to be much elongated. Figs. 2 h and 4 h' demon- 

 strate that such is the case. Their transverse section 

 (fig. 8) is usually a circular one. In the tangential sec- 

 tion (fig. 6) we discover a row of intersected sporan- 

 giophores, h, immediately above each disk, and below the 

 sporangia. Fig. 2 h further explains this arrangement. 

 SER. III. vol. v. D 



