333 



X. On Isoetes japonicaj A. Br. 

 By Cyeil "West, P.jO.S., and H. Takeda, D.I.C._ 



(Plates 33-40 and 20 Text-figures.) 



Eead 3rd December, 1914. 



External MonrnoLOGY. 



ISOETUS JAPONIC A, A. Br., wMcli has a fairly wide distribution in Japan, is the 

 largest in habit of any known species of this genus. The caudex * of an old plant often 

 attains a diameter of 4 cm., and, according to Maldno (22, p. 14G), a diameter of 8 cm. 

 may be reached in very large specimens. The caudex is tri-lobed. In young plants 

 the caudex is sometimes very flat (PI. 33. fig. 6), but in older plants, in which it may 

 attain a height of over 3 cm., it appears roughly cylindrical or napiform with three deep 

 longitudinal grooves (PI. 33. figs. 4, 7). Except in young specimens, each of the three 

 main lobes of the caudex becomes longitudinally subdivided by a number of very irregular 

 shallow fissures (about half as deep as the main grooves), so that, in transverse section, 

 each lobe appears irregularly incised (PI. 38. figs. 56-59). The upper half of the caudex 

 is covered by the * rosette ' of leaves and by the very short leaf-bases. The cells of the 

 latter become slightly thickened and suberized, but they never form a phyllopodium as 

 defined by A. Braun (6, p. 581). The structure designated 'phyllopode' by Makino 

 (I. c. pp. 131, 146) is actually the vagina of the leaf. 



Alonff the hooves and fissures the peripheral ceUs of the cortex also become 



O ^"'-' & 



suberized and form a thin covering of periderm. A similar periderm is formed on tlie 

 lower surface of the caudex. Numerous roots of a dirty brownish colour anchor the 

 plant firmly in the mud at the bottom of a lake or stream. 



Leaves are produced in large numbers; occasionally, more than 200 fully-developed 

 leaves may be counted on a single specimen. These, in plants growing in deep water, 

 attain a length of 1 m. or more. The terminal portion of the leaf is usually aerial and 

 beset with stomata, but leaves which happen to be totally submerged are devoid 



of stomata. 



In transverse section the leaves appear semiteretc-quadrangular with the adaxial 



surface much flattened. The leaf is dilated towards its base, as in all other species of 

 Isoetes, but the wings are comparatively narrow, the width of the vagina at its base 

 never exceeding 2 cm. A few sterile leaves occur on the margin of the leaf -rosette, but 

 the remainder are fertile. In the centre of the rosette of leaves, where a funnel-shaped 



• We prefer the term 'caudex' for the structure usually referred to as the 'stem,' 'rhizome,' 'trunk,' or 



' stock. 



JaSV^ai- 



