370 MR. T. W. WOODHEAD ON THE 
developed palisade about three cells deep, followed by a reduced 
spongy tissue with relatively small air-spaces. 
Fig. 14 is a section of a pinnule from the leaf of a plant 
grown in an Oak wood. The cuticle of the epidermis here is 
thinner, the cells contain few chlorophyll grains, aud the hypo- 
dermis is developed only over the veins. The palisade, though 
well defined, consists only of two layers, and between these cells 
smallair-spaces are frequent. Inthe spongy tissue the air-spaces 
are large. 
Figs. 13-16. 
Fig. 13. Trans. sect. of a pinnule of Pteris aquilina from a plant growing 
under xerophytie conditions on the Gritstone Plateau. 
14. Trans. sect. of a pinnule from a plant growing in the medium shade 
of an Oak wood. 
15. Trans. sect. of a pinnule from a plant growing under the shade of 
Sycamore. 
16. Trans. sect. of a pinnule from a plant growing under the deep shade 
of Beech. 
Fig. 15 is from a frond growing in the shade of a Sycamore 
wood. In this case the cuticle is very thin, palisade greatly 
reduced, a spongy parenchyma occupying a very considerable 
part of the mesophyll. Chlorophyll corpuscles more frequent 
in the epidermis than in fig. 14. The leaf is therefore much 
ihinner. 
