30 PROF. W. C. WILLIAMSON ON THE 



rangia, arranged in about four irregular circles. Each 

 sporangium appears to have its own sporangiphore, of 

 which considerable numbers spring from the upper surface 

 of each disk. 



The Axis. — This resolves itself into a central vascular 

 mass (a) lodged in what is now a clear space (c), but 

 which was at one time doubtless occupied by cellular tissue, 

 the greater part of which has disappeared, either by ab- 

 sorption or decay. This space is surrounded by a cellular 

 cylinder (b) consisting chiefly of a dense form of prosen- 

 chyma, and of which the bractigerous disks are extensions. 

 The form assumed by the central vascular axis (a) con- 

 stitutes one of the most characteristic features of the or- 

 ganism. Its transverse section (fig. 5) may be described 

 as a triangle with concave sides (a 1) and concavely 

 truncated angles (a 2). It consists of a mass of vessels, 

 which are largest in the central portions, and smallest and 

 most dense at the periphery, especially at the angles (a 2) . 

 At each of the latter portions the structure becomes broader, 

 in consequence of the projection of two lateral vascular 

 extensions (a 4) than it is nearer the centre. From each 

 of these projections a line of compressed and disorganized 

 cellular tissue (a 3) extends like a chord across the arc 

 described by the concave side of the triangle, and at a 5 

 we see a similar band stretching across the concavely trun- 

 cated angle. At a' 3 and fl'5 we see clear proof that these 

 have originally been layers of cellular tissue that have 

 closely invested the vascular axis, but which have become 

 detached and shortened during some of the morphological 

 changes which the plant has undergone. Most probably 

 this axis originally occupied the centre of the open cylin- 

 drical space c, but has been drawn to one side, on the dis- 

 appearance of the cellular tissue surrounding it. Fig. 5 b 

 represents a portion of the outer or prosenchymatous 

 cylinder of the axis. In the longitudinal section, fig. 1, 



