AUTUMN IN WOODS 335 



produces the changes which are necessary for its own preservation 

 every year, just at the proper season ? Plants and trees do not fore- 

 see the coming period of cold weather that necessitates the perform- 

 ance of the functions which they execute, and yet they instinctively 

 prepare for the winter in the manner described above. 



Our autumn observations teach us that there are interesting 

 differences in the times and progress of leaf-fall of different species 

 of trees, and also of trees of the same species when exposed to 

 different external conditions. On open ground, where the trees 

 are fully exposed both to the sun's rays and to the cool autumn 

 breezes, the leaves lose their moisture and fall earUer than would 

 the same species in more sheltered situations ; and they retain 

 their moisture and position latest in damp, shady woods. On 

 high hills, where the exposure is extreme, the leaves, which, by 

 the way, do not appear till late in the spring, fall early on account 

 of the low temperature, and consequent decrease of root activity, 

 in the autumn. 



Further, we note that while in some trees, such as the Ash. 

 Hornbeam, Beech and Hazel, the leaves fall first at the tips of the 

 branches, and the defoliation extends faii'ly regularly towards 

 the trunk, in other species, including Willows, Poplars, and the 

 Lime, the branches become bare first at theii- bases, and finally at 

 their tips. 



Even during the depths of winter we may see a number of dead 

 leaves still attached to the twigs of certain trees, notably the Oak 

 and the Beech ; but where we find practically all the fohage 

 remaining on the tree or on special branches of a tree, we may 

 generally assume that the tree, or the branches in question, are 

 dead — that they died during the summer, before the separation 

 layers of the leaves had been formed. We can also understand, 

 from what has been said, why the dead leaves remain attached 

 to a cut branch, and yet fall from the Uving tree from which it was 

 severed. 



In oiu- own country some plants and trees retain their leaves 

 throughout the year, so that we speak of them as evergreens. Many 

 of these include herbaceous plants of a hardy nature, some of which 

 remain fresh and green even in exposed situations, while others 

 grow in more sheltered places. In either case they are plants 

 whose roots remain more or less active in the cold season ; and 

 some of them, especially the evergreen shrubs, have rather thick 

 leaves which contain a considerable quantity of sap, and which are 



