454 Scott and Hill. -— Structure of Isoetes Hystrix . 
Fig. 24 . Callose sieve-plate, shown in longitudinal section of a sieve-tube in the 
foliar bundle, x 1650 . 
Fig. 25 . Sieve-tubes from foliar bundle, showing sieve-areas on the lateral walls, 
x 720 . 
Fig. 26 . Diagrammatic radial section of the base of a sporophyll. Ig, ligule; 
lab, labium ; i, velum ; tr, trabeculae in sporangium ; x, xylem ; ph, phloem of 
the foliar bundle; t, subligular tracheal sheath. 
Fig. 27 . Radial section of rather young leaf, showing base of ligule, Ig; t, 
tracheal sheath, seen on either side of the ligular base, x 160 . 
Fig. 28 . Spinose leaf-base, seen obliquely from above, and from the dorsal side, 
x 8 . 
Fig. 29 . Whole plant, seen obliquely from beneath, after removing the roots 
and spinose leaf-bases; the three furrows and the living sporophylls are shown. 
V 9 
X -j. 
Fig. 30 . Root, in somewhat diagrammatic transverse section, x, xylem; px, 
protoxylem ; ph, phloem; c, cortex, x 68 . 
Fig. 31 . Central part of the root, in transverse section, showing stele and 
intercellular cavity, end, endodermis ; x, xylem ; ph, phloem, x 320 . 
Fig. 32 . Young stele of root, in transverse section, px, protoxylem, the only 
element as yet lignified ; ph, phloem, adjacent to endodermis. X 580 . 
Fig- 33- Young root-trace, close to stele of stem, in transverse section, px, 
protoxylem, two tracheides lignified at this stage; ph, phloem in course of 
development, x about 400 . 
Fig. 34 . Root-stele, in transverse section, at the base of a dichotomy, x, xylem, 
widely expanded laterally; ph, phloem, x about 400 . 
