1907] HOLM—RUELLIA AND DIANTHERA 319 
the nodes, but not directly underneath the leaves, mostly between 
them; the roots are quite thick and long, and branch freely. The 
rhizome represents a sympodium, being terminated by a floral shoot, 
which dies off at the end of the first season; axillary buds occur on 
the rhizome and at the base of the aerial shoot, and these winter over 
and continue the growth of the rhizome at the beginning of the next 
season. 
The germination seems to be unknown, and I regret to say that I 
have never succeeded in studying the young stages of this common 
plant. 
THE ROOTS 
As described above, the rhizome is amply provided with roots 
(secondary), that are quite thick and much branched; they remain 
active for at least two years and represent a combination of storage 
and nutritive roots, but are not contractile. The internal structure 
of these secondary roots exhibits very plainly the features characteristic 
of roots of aquatic plants. The epidermis is very small-celled and 
glabrous. The exodermis consists of three very distinct strata (jig. 8) 
of polygonal cells with the walls slightly thickened and deep brown, 
but with no foldings. The cortical parenchyma is thin-walled and 
consists of about seventeen layers, the cells very regularly radially 
arranged and traversed by wide lacunes from the radial collapsing 
of several of the strata; the outermost layer of the cortex and the 
innermost three usually remain intact. Small quantities of starch, 
but no crystals, were observed in the cortex. The stele shows a thin- 
walled endodermis and pericambium, which was never found to be 
interrupted by the proto-hadrome vessels. Although these roots 
have increased in thickness, the primitive organization is yet quite 
distinct, there being mostly five rays of hadrome with old vessels. 
The cambial arches inside the leptome (jig. 7) are readily visible, as 
well as the very thin-walled young vessels. The leptome is well 
represented, and in several cases it appeared as if there were two 
proto-leptome cells in each strand. A thin-walled conjunctive 
tissue occupies the inner portion of the stele like a central pith. 
No crystals were observed in any parts of these roots, nor any 
sclerotic or stereomatic cells; in the leptome, however, a few raph- 
idines were noticed, but only in some of the roots. By studying the 
