30 BOTANICAL GAZETTE [JANUARY 
the dorsal epidermis is somewhat thicker than the others. 
The inner wall may sometimes show a peculiar bend inwards, 
the lumen of the cell thus becoming diminished, while at the 
same time a wide air space is formed beneath the cell. This 
case was noticed only on the lower face of the blade, and Poul- 
sen found a similar structure, but much further developed, in 
the leaves of Dimeranthus and Actinocephalus. While hairs are 
present on both faces of the blade, stomata are restricted to 
the lower surface. The hairs are small and much shorter than 
those on the rhizome, consisting of but three cells, the terminal 
one being the longest. They are closely appressed to the leaf 
blade and point towards its apex. This form of hair was also 
observed by Poulsen in &. helichrysoides, and its early stage of 
development is represented in his f/. 5, figs. 2-4. 
The stomata occur only on the lower surface, outside the 
mesophyll, and possess very narrow guard cells and subsidiary 
cells, both of which, especially the former, are raised a little 
above the surrounding epidermis. 
The mesophyll in our species constitutes a very uniform struc- 
ture throughout, and the leaf in this respect may be considered 
isolateral. There is no continuous layer of palisade cells on the 
upper face, but the tissue consists of a single stratum, only some 
of the cells of which represent true palisade. Most of the other 
cells are roundish and very loosely connected with one another. 
On the lower face the cells of the mesophyll show a similar round- 
ish form, but the intercellular spaces are not so wide as on the 
upper face. A like structure is represented by the mesophyll 
_ around the mestome bundles, where it is also composed of a 
single stratum bordering on the mechanical tissue. The inner 
portion of the mesophyll is broken down into wide lacunes, one 
between each two mestome bundles, in which are found numer- 
ous diaphragms of star shaped, chlorophyll bearing cells, exhib- 
iting much the same structure as those in the root. 
Attention has been called, in connection with the stem, to 
the difficulty in designating the proper term for the mechanical 
tissue as it is developed in Eriocaulon; and the same is true 



