Boodle.—Anatomy of the Hymenophyllaceae . 459 
dermis (e) } and on the inner side by the protophloem. The 
layer of cells with cuticularized bands in its radial walls will 
here be spoken of in all cases as endodermis 1 , and the layers 
of cells between it and the phloem as pericycle. These 
latter layers, according to Van Tieghem, are partly cortical, 
partly stelar in origin, in Hyme 7 iophyllum % the outermost 
layer being formed of sister-cells of the plicated layer (Stras- 
burger’s endodermis) which is cortical, the inner layer or 
layers being stelar and therefore true pericycle 2 . The ar¬ 
rangement of the radial walls tends to confirm the first point, 
but it appears doubtful whether the inner layers may not also 
be cortical in origin. 
In small rhizomes, such as that of H. tunbridgense , Smith 
(Fig. 16), there is only one layer of cells between endodermis 
and cortex, so that Strasburger’s term £ phloeoterma * 3 might 
be applied to it, as it appears to represent sister-cells of the 
endodermis, which is cortical. It seems, however, convenient 
to remove the morphological meaning from the word peri¬ 
cycle, as Strasburger has done in the case of c endodermis,’ 
and to use it for any cells between endodermis (of Strasburger) 
and phloem. Then when the development has been cleared 
up, one can speak of ‘ stelar ’ or ‘ cortical pericycle.’ 
In Fig. 3, which is a later stage of the rhizome, the phloem 
(p/i) is about fully formed, the protoxylem ( px) abuts on the 
lower xylem-band (/), which is now complete, while the 
differentiation of the upper xylem-band has just begun, only 
two of its tracheides (u) having so far been formed. It is thus 
seen that the lower xylem-band may be fully formed, when 
the upper band has hardly begun to differentiate. The time 
of formation of the latter appears to depend on the proximity 
of leaf-traces. A rhizome of the same age as the above, if 
there had happened to be a young leaf just in front, would 
1 Strasburger (Ueber Bau u. Verricht. d. Leitungsbahnen, p. 484) uses the word 
in this way. 
2 Van Tieghem, Sur le dedoublement de l’endoderme, Journ.de Botan., II, 1888, 
p. 404. 
3 Strasburger, 1 . c., p, 484. 
