272 



STIGMARIA. 



follows that the growth in thickness advances at the same rate in the ring 

 of wood and in the trace, that the secondary elements of the trace at every 

 depth are in direct connection with the corresponding elements of the ring. 

 It is in perfect accord with this that the radial section (Fig. 33 C) shows 

 these large rays as simple intervals 1 , the lower boundary of which is formed 



by the arched convexity of 

 the inner margin of the 

 trace. We see how this ex- 

 tends into the inner margin 

 of the ring of wood ; we see 

 further that it is in direct 

 connection by means of its 

 secondary growth towards 

 the outside with all suc- 

 cessive layers of this wood. 

 Exactly the same structure 

 is found in quite young 

 apices of Stigmariae, only 

 in a smaller form, as is 

 shown by a transverse sec- 

 tion of scarcely i millimetre 

 in diameter, which I saw 

 in Williamson's collection. 

 This author has also pub- 

 lished a figure of a similar 

 specimen 2 . 



The secondary rays 

 show quite normal custom- 

 ary conditions both on the 

 tangential and on the radial 

 section. In the former they 

 may be short and formed of 

 a single row of cells, some- 

 times even be reduced to one 



C B 



FIG. 33. Radial and tangential sections of the ring of wood in the 

 axis of Stigmaria. A tangential section showing the cleft-like primary 

 rays with a strand arising at the lower extremity of each ray, and 

 passing out into an appendage. The apex points upwards. H small 

 piece of the former figure showing the connection of the emerging bundle 

 with the secondary wood of the axis; beneath are seen the outer tra- 

 cheides of the bundle in longitudinal section, higher up obliquely cut 

 through, and quite at the top the inner elements of the same in trans- 

 verse section. C radial longitudinal section of the axis, showing at a 

 the attachment of an appendage to the rind, at l> the point of inter- 

 ruption of the secondary wood lying above the emerging bundle and 

 answering to the primary ray. It is evident that the emerging bundle, 

 the continuation of which through the inner rind cannot indeed be seen, 

 shares constantly in the secondary growth in thickness. All after Wil- 

 liamson (6). A and C slightly magnified, B more highly magnified. 



cell ; they may also be higher and consist of from two to three rows of cells lying 

 side by side. Their form is that of an ordinary brick placed on its longer 

 edge. Authors differ much in their views of the nature of the tissue which 

 filled the central cavity within the ring of wood during the life of the plant. 

 According to Williamson it was simply delicate thin-walled parenchyma, 

 remains of which are in fact sometimes found in the English Stigmariae 



1 Williamson (6), t. 6 ; Binney (1), iv, t. 21, f. 2 ; Hooker (4), t. a, f. 13. 



2 Williamson (6), t. 9. 



