1 1 



ISOETES JAPONICA, A. BR. 



351 



process takes place at the "base of eacli of tlie three main furrows of the caudex. In 

 these regions the primary cortical cells are greatly stretched in a plane at right angles 

 to that of the furrow, whilst a few cells bordering on the stretclied cells become feebly 

 ineristematic, dividing by periclinal walls (PI. 33. figs. 1, 2). The. walls of the stretched 

 cells gradually become suberized and are finally torn apart (PL 33. fig. 3). In this way 

 the main furrows increase in depth. 



A series of transverse sections through the cuudex of an old plant are represented in 

 PI. 38. figs. 55-59. The caudex immediately below the ' leaf-rosette ' has a roughly 

 circular outline, as shown in fig. 55. Immediately below this level the caudex 



t 



begins to assume its trilobed form, but the grooves appear relatively shallow (fig. 56). 

 Sections cut through the caudex at successively lower levels (figs. 57, 58, 59) show the 

 typical tri-lobed outline, the three lobes of the caudex being very prominent in the 

 rhizophore region of the caudex. 



Development, Steucttjre, and Aebangement op the Eoots. 



1. Development of the Boots. 



We were unfortunately unable to investigate the development of the primary root, 

 which was fully developed in the youngest plant we examined. The young roots, which 

 are difi'erentiated from, the primary meristem of the rhizophore, penetrate the cortical 

 tissues of the rhizophore and ultimately emerge from its lower surface. In Isoetes 

 japonica the root never undergoes dichotomy whilst the apex is still embedded in the 

 cortex. 



Our observations on the mode of growth at the apex of the root, so far as they go, 

 confirm the account given by Parmer (14, pp. 51, 52). Distinct histogenetic layers 

 are clearly shown, and the plerome appears to grow from a single initial cell. We also 

 ac^ree with this author that the root in the genus Isoetes is really an early type of. 



adventitio 



2. Structure of the Adult Hoot. 



m ■ r 



The adult roots of Isoetes japonica are essentially similar to those of other species of 

 the genus. They are long and fibrous, and dichotomize repeatedly at a short distance 

 from the caudex (PL 40. fig. 73). They have a dirty-brown colour, which is due to the 

 suberization of their peripheral cells. In a young root, only the outermost layer of cells 

 is suberized ; but in older roots several layers of cortical cells may become suberized. 



The roots bear numerous long unicellular root-hairs, w'hich are most abundant towards 

 the root-apex. 



The general structure of the monarch vascular bundle of the root of Isoetes is well 

 known. It is surrounded by a well-defined endodermis, and occupies an excentric 

 position in the root. The protoxylem, as a rule, is endarch; but a certain amount of 

 irregularity in the position of the first-formed elements of the xylem was observed. The 

 xylem consists of narrow tracheids with spiral or annular thickenings. True sieve-tubes 



second SEEIES. — BOTANY, VOL. VIII. 



3b 



