1908] HOLM—SISY RINCHIUM 183 
interrupted by the protohadrome vessels. This interruption of the 
pericambium was observed only in this species (S. «erophyllum), 
in all the roots examined, but not in any of the roots of the other 
species. 
The hadrome is very conspicuous in all the roots,-and there may be 
as Many as twelve rays with two or three protohadrome vessels in 
each ray; the leptome, on the other hand, consists of very narrow 
strands, in which the protoleptome cell is readily visible (PL, jigs. 
&-11). Although the rays of the hadrome extend to the center of the 
root, the conjunctive tissue, nevertheless, is very conspicuous, and 
is mostly thin-walled except in S. xerophyllum and in some of the 
Toots of S. anceps. 
This structure seems to be characteristic of the slender secondary 
Toots of mature specimens of this genus. In the corresponding roots 
of the seedling of S. angustijolium no exodermis is developed and the 
cortical parenchyma is very thin-walled; the endodermis, on the 
other ‘hand, is very thick-walled, representing a typical U-endo- 
ermis. In these young roots the pericambium is continuous, 
and the stele contains only two hadromatic rays alternating with two 
small groups of leptome. In regard to the structure of the stele, the 
pericambium, and the mestome, the thin lateral roots of mature 
specimens agree with that observed in the secondary ones of the 
seedling; but the endodermis is different, being thin-walled and 
showing the Casparyan spots very plainly (End, jig. 16). 
The structure of the roots of these species is thus very uniform, 
and the only distinction seems to depend upon the structure of the 
Pericambium, which sometimes consists of more than one stratum, 
and which may be interrupted by the protohadrome, as observed in 
S. xerophyllum from subtropical Florida. 
In the tuberous roots of the Central American S. alatwm Hook. 
the Cortical parenchyma represents a very large parenchyma filled 
with starch, and with the cell walls thickened; but otherwise the 
Structure of epidermis, exodermis, endodermis, and pericambium, 
Which is continuous, is identical with that of the species described 
above. The number of hadromatic rays averages about twelve, and 
Pe kitome occurs as exceedingly nartow strands in these tuberous 
S. : 
