ECOLOGY OF WOODLAND PLANTS. 351 
district. It is primarily a humus plant, and its distribution 
depends on the presence of humus. As I have previously shown 
(109), and as Stahl (93) has since independently observed, the 
plant has Mycorhiza on its roots. Stebler & Volkart (94), in 
their study of the “ Matten und Weiden der Schweiz,” made 
a statistical analysis of the species composing the several forma- 
tions there, together with the influence of shade on their dis- 
tribution. With reference to the occurrence of this species, 
they say: “Im Tieflande in Wäldern, in den Alpen im lichten 
Alpenwalde.” We also find it in such situations in the 
Huddersfield district, but we see, on reference to the map 
(fig. 10), that there is a very considerable development also 
in open moorland areas outside our present woodlands. In 
Switzerland, however, it avoids the open sunny situations to 
such an extent that Stebler & Volkart apply to it the term 
“lichtfiirchtend.” This, however, seems too sweeping, for on 
p. 29 of the same contribution they say “Sie kommen in den 
Alpen im Freien vor, weil hier die Bildung des ihnen unum- 
ginglich notwendigen Humus unter giinstigen Bedingungen 
auch im Freien stattfindet." Still, as I have also observed, in 
Switzerland and elsewhere it reaches its greatest development 
in the open woods. In this connection, the observations of 
Wiesner (107) are of interest. In a brief reference to the 
dwarf form of this species (mentioned below, p. 388) which he 
often found in the Yellowstone district of North America, he 
says it occurred “in der Höhe von Thumb Bay im Schatten des 
Waldes und ich verfolgte es so weit, bis es zu verkümmern 
begann, also das Minimum des Lichtgenusses aufsuchte, welches 
ich —.l. gefunden habe." It is very characteristic of the 
16.6 
species in the Huddersfield district to avoid the deep shade of 
the sycamore-elm-beech woods, even though the necessary 
humus is available. 
In view of the considerable evidence of the former occurrence 
of forest on the Moors of the Huddersfield district, as indicated 
below, can it be that its present distribution represents, to some 
extent at any rate, the position of previous open forest? In 
this connection successful attempts have been recently made, 
by Flahault (31), Eblin (27), Sehróter (84), and others, to deter- 
mine the limit of previous forest by means of the present 
distribution of species typically oecurring in woods, and, as Früh 
and Schróter (32) have pointed out, extensive deposits of peat 
nowhere occur outside the tree limit. 
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