Pteridophyten. 109 



West, C. and A. Takeda. On Isoetes japonica A.Br, (Transact. 



Linn. Soc. London. VIII. 8. p. 333-376. PI. XXXIII- XL and 20 

 text figs. 1915.) 



/. japonica is the largest in habit of the species of the genus. 

 It grows in streams or narrow ditches with shallow water. The 

 leaves borne by the stock or caudes are numerous, a Single caudex 

 sometimes bearing more than two hundred. They are relatively 

 large and may be partially or totally submerged. The authors accept 

 the view, held by numerous other botanists, that the stele of the 

 young sporophyte is entirely composed of the united basal regions 

 of the leaf- and root-traces, but that in the adult form the stele is 

 in part purely cauline. They hold, however, that the stele of the 

 adult sporophyte consists of two parts: a vertical cylindrical portion, 

 constituting the stele proper and a fiattened basal portion termed 

 the rhizophoric stele. The rhizophore they consider "a perfectly 

 distinct rootbearing organ of the plant" analogous (not be it noted 

 homologous with) the swollen basal region of the stem of Selaginella 

 spinosa or Pleuronteia. 



The authors examined very carefuUy the growing point of /. 

 japonica j I. lacustris, I. hystrix and /. velata\ they maintain that it 

 consists of a small group of apical cells, thus confirming the conclu- 

 sions of Bruchmann rather than those of other observers. They also 

 found that in all their preparations of /. japonica the cauline tra- 

 cheides develop centrifugally, whereas Scott and Hill describe the 

 developraent of the xylem as centripetal. It is pointed out, however, 

 that some irregularity may be expected in so slow growing a type 

 as Isoetes. The primary xylem consists of scattered tracheides em- 

 bedded in parenchyma and is constantly surrounded by a zone of 

 parenchymatous cells that retain their activity for a long time; it is 

 suggested that this zone was regarded as a cambium by Scott 

 and Hill. 



The primary cortex of /. japonica contains an endophytic fun- 

 gus. There is only one cambium; on its inner side this cambium 

 cuts off a tissue the morphological nature of which has been the 

 subject of much discussion, termed the prismatic layer. Russow, 

 Scott and Hill maintained that this layer consisted of xylem 

 phloem and parenchyma. Wilson Smith doubts whether Q.ny of 

 its elements are phloem, since no distinct sieve-tubes the essen tial 

 Clements of phloem, occur in stem or leaf. Stokey asserts that 

 the cambium does not form phloem. West and Takeda were, 

 however, able to demonstrate the presence of numerous sieve tubes, 

 or rather sieve-cells, since these structures are not syncytic. Occa- 

 sionally, indeed the amount of callus was so great as complelely to 

 fill the lumen of the cell. 



Apparently no secondary xylem is developed in /. japonica; 

 for specimens of all ages were examined and, though it has been 

 described in five other species no trace of it was found in this spe- 

 cies. There is a secondary cortex and a poorly developed periderm. 



Whereas Scott and Hill contend that the growth of the basal 

 region, the rhizophore of the present authors, is entirely due to the 

 activity of the cambium West and Takeda maintain that the growth 

 of the Stele of the rhizophore is acropetal, fresh xylem and phloem 

 being differentiated from an apparently primarj^ meristem forming a 

 narrow band distributed along the whole length of the lower edge 

 of the three lobes of the stele. Though differing in some histological 

 details of development the rhizophore stele contains as does that of 



