314 BOTANICAL GAZETTE [MAY 
sclerotic cells, but with a few cystoliths. The stele is composed 
of three rays of hadrome, and no secondary growth was yet 
observable. 
The capillary, lateral roots are more hairy than the mother root; 
they have an exodermis whose cells are larger than those of the 
epidermis and of the peripheral stratum of cortex. The cortical 
parenchyma is very thin-walled and contains neither cystoliths nor 
sclerotic cells; the stele shows two rays of vessels with thin-walled 
conjunctive tissue; but no stereids and no raphidines were observed 
in these very thin roots. 
The roots of the Acanthaceae have been studied only from a 
relatively small number of genera, and it seems very likely that the 
. structure described above may be observed in several other species of 
Ruellia and in many other genera of the family, as already indicated 
in the works of RADLKOFER, ROULET, Russow, and VESQUE. 
THE RHIZOME 
As stated above, internodes of the rhizome are either very short 
and horizontal,.or stretched and ascending. The latter form shows 
the following structure: the epidermis is perfectly glabrous and 
smooth, with the outer cell walls thickened, and some of the cells 
containing cystoliths; three continuous layers of collenchyma with 
cystoliths surround the cortex, which consists of five strata, whose 
thin-walled cells increase in size toward endodermis and contain 
many cystoliths and raphids, but only a very few sclerotic cells, and 
no starch; the endodermis is thin-walled and the cells are much 
smaller than those of the adjoining cortical parenchyma; a few 
stereids are located inside the endodermis; and the stele shows an 
almost confluent zone of leptome and numerous rays of vessels 
(about ten in each row) with narrow parenchymatic rays; a broad, 
thin-walled pith occupies the central portion of the stele, in which 
cystoliths and deposits of starch were observed. A longitudinal 
section of the internode shows the raphid cells to be very narrow, but 
much longer than the cells of the cortex proper; the cystoliths vary 
in length, those of the collenchyma being longer than those of the 
cortical parenchyma, and obtuse or attenuate at each end. 
