Hill — On the Presence of a Parichnos in Recent Plants . 269 
the lateral expansions of its base. The passages when mature (Fig. 4) 
contain mucilage, and, unlike the parichnos of fossil plants, they do not 
extend into the cortex of the stem, but are entirely confined to the base of 
the sporophyll, their limits seemingly depending on the extension of the 
sporangium. 
Their development follows the normal course for lysigenous muci- 
laginous degeneration. 
The first appearance is indicated by the swelling of the walls of the 
parenchyma, and the gradual disappearance of the cell-contents. This is 
shown by the marked density of the staining, as compared with the sur- 
rounding tissue (Fig. 2). The process of degeneration goes on rapidly, and 
lacunae appear, so that there is formed a central cavity (Figs. 3, 4, 15 and 
1 7). This cavity gradually extends radially, ultimately resulting in an 
extremely well-marked mucilage-canal more or less circular in outline. 
As regards the sterile leaves, Isoetes Hystrix does not form many, and, 
apparently, they do not possess the parichnos-strands. 
Unfortunately it has not been possible to examine satisfactory material 
of any other species of Isoetes with the exception of Z lacustris ) which 
plant does not show any sign of the structure in question. 
Other living representatives of the Lycopodineae have naturally been 
examined. 
In the case of Lycopodium , Hegelmaier 1 showed that the leaves of 
Z. inundatum and Z. alopecuroides are traversed throughout their whole 
length by a mucilage-canal, which enters the cortex of the axis where it 
ends blindly. In the young leaves, these canals are represented by thin 
strands of parenchymatous tissue somewhat merismatic in appearance. 
De Bary 2 draws attention to similar passages occurring in the marginal 
expansions, on the dorsally winged sporophylls, of Z. annotinum . 
Jones 3 corroborates Hegelmaier regarding the presence of the mucilage- 
canals in Z. inundatum , and states that these structures were not observed 
in the vegetative leaves in the other species examined, viz. Z. alpinum , L., 
Z. annotinum , L ., Z. cernuum , L., Z. Chamaecyparissus , A. Br., Z. clavatum , 
L., Z. complanatum , L., Z. Dalhousiea num , Spring., Z. nummularifolia , 
Blume., Z. obsciirum , L., Z. Phlegmaria , L., Z. Selago, L., Z. serratum , 
Thunb., and Z. squarrosum , Frost. 
Many of these species have been examined by the writer, who cor- 
roborates the observations made by Jones regarding this point, with the 
exception of the case of Z. cernuum . Although the mucilage-canals are 
frequently absent from the vegetative leaves, they are often present in the 
1 Hegelmaier, Zur Morphologie der Gattiwig Lycopodium. Bot. Ztg., 1872. 
2 De Bary, Comparative anatomy of the Phanerogams and Ferns. Oxford, 1884. 
3 Jones, The morphology and anatomy of the stem of the genus Lycopodium. Trans. Linn. Soc. 
Lond., 2nd ser., Bot., vii. 
