SN Le, a 
OF THE BRACKEN IN RELATION TO ENVIRONMENT. 663 
In a patch of bracken apparently under uniform external 
conditions, one leaf was conspicuous in having more xerophytic 
characters than the adjacent leaves. It was found that the 
petiole had been partly severed on one side (evidently when 
young). The conduction of water from the soil was doubtless 
intertered with by this injury, and one is led to conclude that the 
different character of the leaf was due to reduction of its water- 
supply. 
The following is a case often met with. Bracken was growing 
crowded and beneath oak-trees, where the shade was not very 
dense. The plants nearly out of shelter (just outside the trunks 
on the edge of the belt) had hard leaves, while leaves occurring 
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Structure of different parts of the same leaf. ; 
Fig. 1, exposed pinna; fig. 2, sheltered pinna, X about 195. 
further in were, on the whole, fairly soft ; but the more exposed 
parts of these leaves were decidedly more xerophytic and had 
long sori. Where the bracken was growing densely, it was found 
that those leaves, or lower parts of leaves, which were well covered 
by the top growth were soft and either sterile or with short 
sori. . . 
A still better example of the same kind may be described in 
greater detail. A leaf about 6 feet high had grown up through 
a rather dense bush consisting of gorse, hawthorn, and bramble. 
The lower part of the leaf, immersed in the bush, was of the sott 
type; its structure is illustrated in fig. 2. The uppeninos bione 
of the leaf had overtopped the bush and were well ope ve " 
sun and wind. Fig. 1 shows that this portion of the leat has 
