ECOLOGY OF WOODLAND PLANTS. 379 
stereom-band 2-3 cells deep, and an almost complete stereom- 
plate is formed in the centre between the inner steles. On the 
steep slopes in the transition region every gradation between 
these extremes is found as we pass from the dry exposed 
gritstone summit over the moister sheltered areas of the shales 
and clays, the rhizomes reaching their maximum development 
aud possessing the greatest storage capacity in the moist Oak 
woods in moderate shade. The observations of Blackman (5 A), 
Brown (9 4), and others show that shade-leaves assimilate more in 
the shade than sun-leaves in the shade. Under these circum- 
stances, much stareh will be produced by the shade-plants and a 
considerable storage-tissue required. A comparison of the 
rhizomes of Pteris growing under different conditions shows, as 
we have seen, that under moderate shade the rhizomes attain their 
greatest development and possess the greatest amount of storage- 
tissue ; while plants growing under xerophytie conditions have on 
the whole thinner rhizomes, but a great development of stereom, 
and therefore a correspondingly reduced starch-storage tissue. 
The maximum of storage-tissue, in proportion to the diameter 
of the rhizome, I found in plants growing in deep shade. 
SCILLA FESTALIs, Salisb. Bluebell or Wood Hyacinth. 
This species obtains its maximum development in this district in 
the moist Oak and Sycamore woods on the Coal-Measure shales 
and clays. <A typical leaf of a plant from these woods (fiz. 33, 
p. 380) is clear green, and characterized by the cuticle of the 
upper epidermis being fairly well developed and very slightly 
corrugated (fig. 34). Beneath this are two rows of cells with 
abundant chlorophyll corpuscles, and in the remaining cells the 
corpuscles are very few or absent, except a single layer beneath 
the lower epidermis where they are abundant. Air-spaces are 
well developed in the mesophyll, and running through the centre 
of it is a nearly continuous line of clear rounded cells. Between 
the three bundles, on either side of the midrib, are lacune. 
The position of each lacuna is indicated at an early stage in 
development by a colourless rounded cell. ‘This increases 
considerably in size, is very thin-walled, and eventually breaks 
down; in some cases, especially adjacent to the midrib, some of 
the neighbouring cells are involved. 
Plants growing in the deep shade of a Beech wood present a 
sickly appearance, often showing traces of partial etiolation, 
