14 THE STEM. 



their growth late in the season, will add to their leaders from 15 to 

 18 inches in the short space of six or eight weeks. Ahii-tia /)<>H<i/<t*it 

 makes an average growth of from 21 to 27 inches annually, and Finn* 

 i-wliafa* even more. The rate of growth varies in each kind 

 according to the soil and situation; it is also influenced by the 

 state of the season, being greater or less according as the temperature 

 is higher or lower than the average mean. Every annual increase in 

 height is, of course, accompanied by an increase " in the diameter of 

 the trunk indicated by one ring. 



Theoretically, the trunks of coniferous trees might increase in size 

 and height indefinitely, were there no counteracting^ causes at work to 

 check and finally to arrest the progress ; but such sooner or later are 

 sure to arise, and among the principal are undoubtedly the gradual 

 exhaustion of the soil in which the tree is growing, and the choking 

 up of the channels of circulation by the deposition of insoluble 

 matter taken up by the roots. The functions of the various organs 

 become enfeebled by age, as they do in the animal frame, although the 

 period of the life of the one is in most instances immensely prolonged 

 compared with that of the other, so that the cause of decay is so 

 much the slower in its action. The vigour with which coniferous 

 trees increase in size during the earlier period of their existence is 

 sensibly diminished in process of time, till at length the counteracting 

 causes balance the growing power ; the tree has then reached its full 

 maturity ; the period of decay sets in which is never permanently 

 arrested till the death of the individual and the subsequent decomposition 

 of its tissues is complete. 



X cross section of the trunk of a large coniferous tree shows that 

 the annual rings nearest the central pith are the broadest, and that 

 their width diminishes as they recede from the centre to the bark. 

 In trees felled in Great Britain the diminution is not symmetrical ; a 

 ring of a certain width in any part of the section is not precisely 

 so much narrower than the one within it, or so much broader than 

 the one immediately without it. On the contrary, the irregularity 

 in this respect is very considerable, so that a ring is often found 

 which is broader than the one nearer the centre. This irregularity is 

 believed to be due to climatic changes. During a long and warm 

 summer a coniferous tree will make much more growth than during a 

 wet and comparatively cold one, and it is not improbable that the 

 fluctuations of the seasons are represented by the different widths of the 

 rings. But in regions like California and that of the Himalaya where 

 the alternation of seasons is regular and the average annual tempera- 

 ture and rainfall almost constant, the diminution in breadth proceeds 

 very symmetrically ; but there are throughout the sections circular 

 spaces of considerable breadth in which there is an appreciable 

 uniformity in the width of these annual rings, so that the gradual 

 diminution is not perceptible unless a series of the inner rings is 

 compared with a series nearer the circumference. The general principle 

 is, however, never departed from : the rings more remote from the 



* The growth of Pinus rod-iota in the warm and more equable climate of Xew Zealand 

 is very rapid. A correspondent in the Canterbury district informed Messrs. Veitch that 

 he had measured shoots of the preceding year's growth nine feet long ; the average growth 

 of a number of trees in a plantation was quite six feet. Its growth is equally rapid 

 in South Australia, Victoria, and other sub-tropical lands possessing a moderate rainfall 

 similar to that of South California. 



