1893.] The Roots of Ranunculacee. 45 
present a very peculiar structure, as compared with the struc- 
ture of the roots of the other plants of the order. | will 
endeavor to make this clear by describing the structure of 
the older roots of Thalictrum diotcum.1* The smaller, younger 
roots of allof these plants show the usual radial root structure, 
and do not deserve particular description. This plant, and 
especially Thalictrum polygamum, has a numerous cluster of 
large fibrous roots, and it is the structure of these roots that 
will be described. A cross section of these roots shows a very 
large central cylinder enclosed by avery regular endoder- 
mis composed of very small square cells. The xylem ves- 
sels are in a rather compact cluster at the center, and radi- 
ating from this are from two to four rays of phloem, each ray 
of two or more separated groups, the cells of which are very 
small and thin walled. Sometimes the central xylem presents 
the same number of short rays as the phloem The greater 
mass of the central cylinder is occupied by very regular and 
generally angular cells, the walls of which are often slightly 
thickened. The cortex is very small in proportion to the cen- 
tral cylinder and is of roundish loosely packed cells. At 
first an epidermis is present, but most of these roots gathered 
in the fall had exfoliated their epidermis together with all 
but about two rows of very loosely packed cortex cells. This 
leaves the endodermis as the real protecting organ, and per- 
haps accounts for its rather peculiar appearance. The walls 
of the endodermal cells are generally cutinized. 
_ The structure of a younger root of 7. polygamum is shown 
In plate 111, fig. 20 and plate Iv, fig. 28. The style of struc- 
ture which has been described for the older roots of 7. dioz- 
‘um was also observed in the older roots of T. polygamum 
and Aguilegia Canadensis, and in the tuber-like roots of 
Anemonella thalictroides, though with minor differences in 
each case. I have not examined the roots of J/sopyrum 
biternatum, but from Prof. Hargitt’s description I should say 
It too belonged in this class. 
From the above descriptions it will be seen that Olivier’s 
Statements concerning the genus Ranunculus are borne out 
my observations, for in only one species, Ranunculus 
Sceleratus, could [| discover any great change of structure 
through secondary development. The exfoliation of the 
Cortex of the Thalictrums is spoken of by both Olivier and Ma- 
Plate Iv, fig. 29, 
