265 



latter having fewer stomata upon the upper surface and none 

 at all upon the lower surface.^ 



4. Trachyphylkim. 



The three species which have been examined, agree in 

 (1) the structure of the hydathode (it opens upon the upper 

 surface of the leaf, with flattened or highly convex epithema; 

 hydathode-cavity absent), (2) the structure of the hairs (they are 

 everywhere irregularly-multicellular and retain this feature, either 

 they have, or are without, an apical gland, — in contradistinc- 

 tion to the sections Boraphila, Nepliroi^hyllum, Dactyloides], 

 and (3) the cells of the spongy parenchyma are very little or 

 not at all branched. — The three species differ most in the 

 form of their leaves, but are separated also by other, smaller 

 differences. 



The chief structural features useful in diagnosis are the 

 following: — 

 Leaves: — 



toothed at the apex, with three acute teeth: S. tricuspidata. 

 entire : — 



margin hairy along the lower half of the leaf: S. 



aizoides, 

 margin hairy along its whole extent: S. flagellaris. 

 Hairs : — 



irregularly-multicellular marginal hairs: S. aizoides, 

 glandular hairs with irregularly-multicellular stalks: 6\ 

 flagellaris, 



(1) with globular head: S. flagellaris, 



(2) with club-shaped head: S. tricuspidata. 



Besides the principal form I also examined specimens of the variety 

 ' palmata from Thingvellir in Iceland (June 13, 1895). The latter is very 

 remarkable by reason of its agreeing in almost all points with S. hypnoides 

 in regard to leaf-anatomy; the only difference being that a few of the 

 marginal hairs of the leaf are glandular. 



