1908] HOLM—ALPINE GRAMINEAE 433 
bium. Such discrepancies often occur, but they are hardly of any im- 
portance. 
In the alpine Gramineae from Colorado the root structure is 
very uniform. The epidermis is hairy in all the species; a thin- 
walled exodermis was observed only in Agropyrum violaceum. The 
cortical parenchyma is mostly thin-walled and solid, but a radial 
collapsing was noticed in the species of Poa, with the exception 
of P. alpina, in Trisetum, and in Deschampsia. In the species of 
Agropyrum the peripheral strata of the cortex are stereomatic, and 
persistent in comparison with the inner, which are thin-walled and 
collapsed. The endodermis is generally thick-walled (figs. 1-5, End), 
Tepresenting a typical U-endodermis, or an 0Q-endodermis, as was 
observed in specimens of Poa alpina from bowlder fields. The 
pericambium was found to be continuous in all the species, and it is 
generally thin-walled; but in the species of Agrostis (fig. 2), Calama- 
grostis, Trisetum, and in Poa gracillima it is more or less thick- 
walled. It consists mostly of a single layer, but in the species of 
Agropyrum (fig. 5) and Avena two or three layers are developed 
outside the proto-hadrome vessels. ‘The number of hadromatic rays 
is of course very variable; in the thick roots of Trisetum, Deschampsia, 
Calamagrostis, Avena, and Agropyrum there may be as many as 
teen rays, but with mostly a single proto-hadrome vessel in each 
Tay. In the species of Agrostis and Festuca the hadrome extends to 
the center of the stele, while in the others a central pith is developed. 
This pith is quite broad, and often conspicuously thick-walled, as in 
Trisetum, Agropyrum, Avena, and Calamagrostis. 
It is interesting to note that in some cases the root structure 
Corresponds with the nature of the substratum. For instance, In 
Poa Lettermanni, which I found growing in wet moss near the 
Snowbanks, the root structure resembles that of a hydrophilous 
Plant, with open cortex, thick-walled endodermis, and thin-walled 
Pericambium. In the species of Agropyrum from very. dry, stony 
Soil, the peripheral strata of the cortex are stereomatic. In Cala- 
Magrostis purpurascens from similar stations there is a very compact 
‘ortex, a heavily thickened endodermis, a thick-walled pericam- 
bium, and a broad central, very thick-walled pith. A similar, very 
Solid structure is also characteristic of the species of Festuca and 
