. GROWTH OF WOOD IN DECIDUOUS AND EVERGREEN TREES. 57 



these I hope to undertake in future years.* At present all that we can safely 

 say is that the increase of wood in evergreen trees from the beginning of 

 spring till the end of May probably exceeds on an average that of every subse- 

 quent month. Table VII. shows that it did so in the case of the six selected 

 trees in 1880 and 1882, also in the eighteen trees measured in the latter year. 

 In 1881 the observations are incomplete, as separate measurements were not 

 made for May and June, but August — with 31 per cent. — has a strong claim 

 to the highest place, due I believe to exceptional circumstances. 



One of the most remarkable conclusions that may be drawn from the three 

 years' monthly observations on evergreen trees, as a class, is that they appa- 

 rently accomplish the greater part, and sometimes much the greater part, of 

 their growth by the end of June. Thus in 1880, 64 per cent., in 1881, 51 per 

 cent., and in 1882, 68 per cent, of the annual increment of the six selected trees 

 was finished by that date, and the increment of the eighteen trees measured in 

 1882 was almost identical with that of the six in the same period, amounting to 

 63 per cent. Apparently then it is not heat alone which regulates the growth of 

 wood in many evergreen trees. By some inherent vital power they complete the 

 greater part of their growth before the commencement of the two warmest 

 months in the four which constitute the growing period, or else their vital power 

 is so exhausted in the early part of the season that growth cannot be carried on 

 with vigour when the real heat of summer comes on. 



In conclusion, it must be allowed'that further observations, both on deciduous 

 and evergreen trees, are required to determine which is the best growing month 

 in each class. At present the indications are in favour of July for the former 

 and May for the latter, if the whole, or nearly the whole, of the growth hitherto 

 ascribed to that month really belongs to it.* 



3. Monthly Increase in certain Species of Trees. 



There is considerable variety in the vigour of growth in different species 

 both of deciduous and evergreen trees in the different months of the growing 

 season. My observations on this point indeed, on any considerable number of 

 trees, extend only to a single year, but the results are sufficiently striking to 

 deserve attention. In Table VIII. are given the percentages of monthly growth 

 in seven species, which, either from the number of specimens under observation, 

 or from the certainty of their measurement, yield the most reliable results. 



The Hungary oak begins to grow earlier than any other of the deciduous 

 trees under observation. In the backward spring of 1880 the three specimens 

 marked in the Botanic Garden were well clothed with foliage on the 15th May, 



* Since this paper was read, the spring measurements for 1883 show a growth in April amounting 

 to two-fifths of that in May in twenty evergreens under observation. It appears probable therefore that 

 June is the month of greatest growth for evergreens. 



