434 BOTANICAL GAZETTE [DECEMBER 
Agrostis, inhabitants of dry soil among bowlders. The roots of 
these species thus show in general the structure of xerophytes. But 
in Poa alpina no such distinction seems feasible, since the struc- 
ture is identical whether the specimens are from wet soil in thickets 
of willows along mountain brooks, or from dry soil among bowlders. 
The culm 
In describing the structure of the culm, attention must be given 
to the distribution of the mechanical tissue (stereome), to the minor 
structure and disposition of the mestome strands, and finally to the 
structure of the cortical parenchyma. In the character of the stereome 
our alpine Gramineae represent the type in which a circular band of 
this tissue (in cross-sections) is in contact with all the mestome 
bundles; it is the eleventh type of SCHWENDENER’? and is the one most 
frequently observed in the Gramineae. While the principal feature 
of this type is that all the mestome strands are in contact with the. 
mechanical tissue, some modifications are to be observed in regard 
to the relative development or strength of the stereome, especially n 
cases where the mestome bundles occur in different sizes, and in 
more than one circular band. Five very distinct modifications Lae 
observed in our alpine species, which may be readily distinguishe 
by the accompanying figures, which I have drawn in a schematic 
way. The black represents the stereome; the peripheral white zone 
the cortex; the central white zone the pith; the orbicular and oval 
rings the mestome strands. 
In these figures, A represents the most simple structure, where 
there are only five mestome strands, all the same size and outline 
(oval), and all imbedded in the stereome, which extends to epidermis, 
thus forming a strong, hypodermal support outside the leptome 
(Agrostis canina, var.). In B there are four large, oval mestome 
strands, alternating with four much smaller ones, which are orbicular 
in transverse section, and they are all surrounded by stereome, whi ; 
only extends to the epidermis outside the larger ones (Poa Letter apes 
P. alpina from Long’s Peak, and Agrostis varians). In C ( a 
rupicola) there is also one band of mestome bundles, composed ° 
t0SCHWENDENER, Das mechanische Princip im anatomischen cn in 
Monocotylen 60. Leipzig. 1874. 
