Holm, Some new anatomical characters for certain Gramineae. 131 



diverse localities, vre liave, so far, observed tliis same sheath in 

 DO less tHan four subgenera : Eucyperus^ Pycreus, Mariscus and 

 Diclidium, thus if Cy}jerus should be divided into CJiloro- and 

 Eu-cyjjerus, each of these would actually become an alliance of 

 veiy diverse types, of which several paralel forms would liave to 

 be separated and refered, some to Cliloro- others to Eu-cyperus. 

 In this instance the morphological characters should not be under- 

 estimated, even if the anatomical characters be ever so pro- 

 minent. 



It is differeut, however, with Äristida, where excellent mor- 

 phological characters accompany the anatomical distinction, and 

 it has surprised us, that the plumose-awned Stipae appear to be 

 anatomically inseparable from the others ; we had expected to find 

 in these Stipae diversities in structure analogous to those observed 

 in Äristida. 



Thus is the presence of this double sheath and the absence of 

 a mestome-sheath the most conspicuous character, by which the 

 North American and some other species of Äristida are distinct 

 from their allies. But otherwise, as we have seen above, the 

 leaf-structure in general is much the same in all of these. The 

 more or less deeply furrowed surface of the blade; the development 

 of epidermis into bulliform cells between the ribs, but not above 

 the midrib ; the presence of papillae or hairs beut over the furrows 

 with the stomata; the palisades arranged radially around the 

 mestome-buudles and fiually the distribution and relative develop- 

 ment of the stereome, all these characters seem almost uniformly 

 developed in these species with but a few exceptions. The co- 

 lorless tissue, the function of which is generally explained as 

 being for the storage of water, is on the other band very une- 

 qually represented in these plants; it is developed in many and 

 located underneath the bulliform cells in the furrows, but it lacks 

 in Stipa, Oryzopsis, Eriocoma etc. several of which are among 

 the most frequently associated with Äristida, besides being among 

 its nearest allies. 



If we finally consider the habit of these plants, it does not 

 seem as if anj special type is characteristic,, neither among the 

 species from the plains, the prairies or the fields. Caespitose and 

 stoloniferous species occur together ; the culms may be simple or 

 much branched with numerous lateral inflorescences ; the leaves 

 may be almost vertical or horizontal, flat or conduplicate, at least 

 when dry, but usually with power to open, when the atmosphere 

 becomes moist; the leaf-sheaths may be narrow or much inüated, 

 thus partly enclosing the inflorescence, as in the pistillate plant 

 of Buclüoe, in Munroa, Sporolohus cryp)tandrus , vaginaeßorus, 

 asper etc., and a similar case is also recorded by Warming*) 

 as characteristic of several Gramineae from sandv sea-shores in 

 Denmark. 



*) Warming, Eug, De psammophile Formationer i Danmark, (Vidensk. 

 Jledd. Naturhist. Forening 1891. p. 199.) 



