44 The Botanical Gazette. (February, ' 
cribe the two forms of structure as found in the young and © 
old roots of Clematis Virginiana.‘° In the young root (fig. — 
25) the are as marked x are the primary xylem rays and fh the 
phloem masses, the scells of which are not drawn, the em 
dodermis is seen at ez, the cortex at c, and the epidermis ata — 
The structure of the older roots is represented in fig. 24 in ~ 
which the original xylem rays are at +, and secondary xylem 
rays, x’, have been developed so as to be more prominent than _ 
the original rays, and have pushed the phloem, p/, towatd 
the endodermis; at a is what appears to be meristematic tis _ 
sue, peripherad of which are the phloem cells. All within 
the dotted line is of thick walled cells, probably a part of the 
secondary xylem. The endodermis has become somewhat _ 
modified though not as much so as in many of the roots a 
this class, but the central cylinder is notably larger in pro- 
portion than in the smaller roots, as the figures well show. — 
certainly a perennial, do not show secondary change. 
I should make a third class of structure for Zhai” 
diotcum, Sf halictrum polygamum, Anemonella thalictrom™ 
and Agutlegia Canadensis, for the larger roots of these plan 
Plate tv, figs. 24, 25, . 
1Plate 1, figs. 15, 16. 
"Plate mu, figs. 19, 21. 
