Liliales. 



349 



In T. coccinea there is as a rule 9( — 11) vascular bundles 

 (Fig. 2), in T.palustris 11( — 13). In the first-mentioned the 

 leaves are often more flaccid (Fig. 1, D), frequently partly 

 decumbent, especially in exposed piaces, whilst they, in the 

 latter, always are rigidly erect. 



The structure of the le af is in all essentials identical 

 in the two species. The sheath is constructed like a normal 

 leaf, above this the leaf is isolateral, has an equal right and 

 left side, an upper and lower margin (Fig. 3). The epider- 

 mis consists, except on the upper 

 (inner-) side of the sheath, of ra- 

 ther small cells, the walls of which 

 are slightly undulating, highly 

 thickened, porous and covered 

 by a well-developed cuticle which 

 also spreads to the guard-cells of 

 the stomata (Fig. 3 5, D). The 

 stomata are arranged longitu- 

 dinally, their slit is quite diminu- 

 tive, the intercellular cavity 

 beneath them is quite small. The 

 base of the sheath consists of 

 hyaline parenchyma ; a little higher 

 up, on the morphological lower 

 side, we find the chlorophyll 

 tis SU e consisting of several lay- 

 ers of cells, whilst the upper side is constantly non-chlorophyl- 

 lose. Above the sheath the chlorophyll tissueis homogeneously 

 developed on both sides, the non-chlorophyllose part occupy- 

 ing the centre of the leaf, extending right to the tip of the 

 leaf (Fig. 2, 3, A, B). In contradistinction to Narlhecium 

 (vide Raunkiær) no air-chambers are found in the chloro- 

 phyll layer on transverse sections. 



Fig. 2. T. coccinea. Nordre 



Stromfjord, Greenland. 

 a — e show sections in various 

 height through a foliage 

 leaf. The xylem of the vas- 

 cular bundles is dark. The 

 dotted line shows the bound- 

 ary between the chlorophjil 

 tissue and the aqueous tis- 

 sue; a, showing the basal 

 part of the sheath, has no 

 chlorophyll. 

 (Drawn by M. P. P.) 



xxxvii. 



23 



