THE SOCIAL HABIT 179 



line followed by the rain water when trickling down the trunk. 

 Many species form a carpet. Some grow on stones, covering them 

 entirely. These are generally very minute, and many of them 

 belong to the genus Weissia. Others are found at the foot of trees 

 growing on the exposed roots. One of the most beautiful is the 

 Fern Moss ; it is very abundant in the west and south of England, 

 reaching perfection in the damp woods of Devonshire. The 

 Hair Moss (Polytrichum) (Fig. 26) and several species of the genus 

 Mnium (Fig. 22) are characteristic of woods. 



Besides Mosses, many Ferns contribute to the carpet of a wood. 

 The Shield, the Oak, the Polypody, and the Beech Ferns are the 

 most common, and in Pine and Oak-Birch woods, the Bracken. 

 The Shield Fern (Aspidium) and the Polypody both have their 

 sporangia arranged in circles on the under side of the frond ; the 

 Polypody, however, is a very much smaller fern than the Shield 

 Fern, with thicker wavy leaves, whilst the Shield Fern has very 

 thin leaves and the fronds form a circular tuft two or three feet 

 high ; those of the Polypody are not more than a foot in height, 

 and often less. The Oak Fern is also a Polypody, belonging to 

 moister situations than the common Polypody ; its fronds have 

 long stalks, and the leafy part may be four to six inches long. 

 The Lady Fern is not unlike the Male Shield Fern, but its stalk 

 is less scaly than that of the latter, and its fronds reach 

 the height of two or three feet. The Hard Fern (Lomaria or 

 Blechnum) is very common in some districts, and is one of the 

 best known ferns where the climate is not too dry, or where lime 

 is absent from the soil. 



Thus the vegetation forming the carpet of a wood is of extra- 

 ordinary interest. It is never the same for long together, but 

 varies almost with each month of the year : in the autumn it is 

 the Fungi that claim attention ; in the winter, the Liverworts 

 and Mosses ; in the spring, the early Flowering Plants. At all 

 seasons the trees with their bark-growth, their buds, their branch- 

 ing, their colouring afford a fascinating study. Moreover, the 

 vegetation differs with each wood, owing to the difference in the 

 humus and amount of moisture, and the humus depends on the 

 dominant tree. To compare woods with each other, noting the 

 resemblances in the presence of great diversity ; to try to account 



