266 



BRITISH PLANTS 



The undergrowth present depends upon : 

 1. The amount of light coming from above. Some 

 trees intercept much light and cast a deep shade 

 e.g., beech and sycamore and under these the vegetation 

 is scanty or absent ; others allow a considerable amount of 

 light to penetrate through their loose crowns e.g., oak, 

 ash, birch and this supports a rich and varied flora, 

 both bushes and herbs. This is well seen in the accom- 

 panying maps (Figs. Ill, 112), taken from Woodhead's 

 paper on The Ecology of Woodland Plants, which show 

 clearly that the distribution of the bracken is determined 

 solely by the amount of light present, the soil varying in 

 different parts of the wood from a stiff clay to a light sand. 



Fio. 111. MAP OF A WOOD, SHOWING DISTRIBUTION OF TREES. (AFTER 



WOODHEAD.) 



oak dominant. OO Fagus -sylvatica. 



d L~ Ulmus montana. AA Acer Pseudoplatanus. fa ^ conifers. 



2. The nature of the soil, the presence of mild or sour 

 humus, and the amount of water present. The soil-factor 

 usually determines the kind of plant which is found, and 

 the light-factor decides its abundance. 



The herbaceous or ground-vegetation in woods consists 

 chiefly of shade-plants, their stems being tall or elongated, 

 and their leaves often large. They are nearly all peren- 

 nials, hibernating by rhizomes, tubers, or bulbs ; annuals 

 are rare. In the humus of moist, shady woods a few 

 colourless saprophytes grow (Neottia, Monotropa), but epi- 



