312 BOTANICAL GAZETTE [MAY 
Ruellia belong to the second type, the additional, which develop spon- 
taneouslyfupon the uninjured plant, and which constitute an impor- 
tant addition to the subterranean vegetative organs. This category 
of root-shoots is the one that is best known and most frequent; our 
species of Apocynum illustrate this manner of propagation in a 
striking degree, and I have seen as many as ten flowering stems of A. 
cannabinum developed upon one single root;® it is also the kind so 
commonly met with in Sassafras, Rhus Toxicodendron, Comandra, 
etc. It may be stated at the same time that the development of 
additional root-shoots appears to be characteristic of plants in certain 
localities; for instance, on the plains of Colorado I noticed a remark- 
ably large percentage of plants of various families that exhibited this 
peculiar mode of propagation. 
THE ROOTS 
In mature specimens the secondary roots are quite thick, somewhat 
fleshy, and of a light brown color. The epidermis is thin-walled and 
somewhat hairy; it covers an exodermis of one layer, which is also 
thin-walled and whose cells show the same lumen and shape as those 
of the epidermis. The cortex is differentiated into three distinct 
zones: a peripheral of three layers of more or less thick-walled cells 
with many cystoliths; about nine strata inside the peripheral, which 
consist of thin-walled cells with rhombic intercellular spaces, and of 
very thick-walled sclerotic cells (figs. 1, 2) besides cystoliths, while no 
raphids were seen, and no deposits of starch; the innermost stratum, 
represented by a thin-walled endodermis of small cells and with the 
Casparyan spots very plainly visible. 
The sclerotic cells are very characteristic and readily noticeable 
by their narrow lumen and porous walls; they are stained bright 
yellow by chlor-zinc-iodin. Similar sclerotic cells are known also 
from the roots of Thunbergia annua, according to ROULET (p. 343): 
The cystoliths of the Acanthaceae are very well known, and “have 
been described very carefully by SoLEREDER (p. 697). They vary 
somewhat in outline, from almost quadrangular to fusiform with the 
© That the horizontal shoot-bearing roots of Apocynum have been mistaken for 
“horizontal rootstocks” may be seen in MILLER: Dogbanes of District of Columbia 
Proc. Biol. Soc. Washington 13:79. 
