40 ON THE ORGANIZATION OF VOLKMANNIA DAWSONI. 

 INDEX TO PLATES I., II., and III. 



( VOLKMANNIA DAWSONI.) 



a. Central vascular bundle of the axis. 



b. Outer cellular wall of the axis. 



c. Middle tissue of the axis, probably cellular. 



d. Verticillate bractigerous disks. 



e. Sulcated inferior surface of the peripheral part of the bractigerous disk, 

 indicating its approaching division into succulent bracts. 



/. Thick primary bracts, resulting from the division of the bractigerous 

 disks. 



f. Middle portion of the bracts, where they exhibit an oval transverse 

 section. 



/'. Extremities of the depressed bracts, exhibiting an oblong linear trans- 

 verse section. 



g. Walls of the sporangia. 

 h. Sporangiophores. 



x x (fig. 1). Line of the transverse section fig. 3. 



yy. Line of the transverse section fig. 4, only from a part of the strobilus 

 on the right hand, where sufficiently perfect to cross the line of section. 

 z z. Line of the tangential section fig. 6. 



PI. II. 



Fig. 1. Vertical section through the centre of the axis. 



2. Oblique tangential section, crossing the bractigerous disk at its 

 upper part, and passing between the outer cellular cylinder of the 

 axis and its central vessels inferiorly. 



PI. I. 



Fig. 3. Slightly oblique transverse section, made in the plane of the line 

 x x of fig. 1. 

 4. Similar section, made in the plane of the line y y, fig. 1. 



PI. III. 



Fig. 5. Enlarged representation of the central vascular axis of fig. 3. 



6. Tangential section, made in the plane of the line z z of fig. 1. 

 being intermediate between the section fig. 2 and the exterior of 

 the strobilus. 



7. Portion of the lowest bractigerous disk on the right of fig. 2, giving 



off a sporangiophore (h) from its upper surface, and exhibiting 

 the prosenchymatous structure of the former organs. 



PI. II. 



Fig. 8. Transverse section of a sporangiophore. 

 9. Three aspects of the spores. 



The same letters are employed to indicate identical structures in all the 

 above figures. 



