64 Dr Christison oyi the Oirth of 1 rees. [sess. li. 



and Abies Lowiana, the predominance of the first half-season 

 is well marked. 



In one species, Cedrus atlantica, tlie two half-seasonal 

 growths were almost equal. 



In two, Taxus baccata and Cedrus Deodara, the increment 

 of the second lialf was considerably greater than that of the 

 first. 



The extreme differences were between the Araucaria (73 

 and 27 per cent.) and the Deodar (34 and G6 per cent.). 



The result in the case of the Deodar is the more remark- 

 able, because it was the earliest of the measured species to 

 show activity in spring. In the years 1885 and 1886 I 

 measured the length of the new shoots in all my marked 

 evergreens on the 30th April and 31st May, and those of 

 the Deodars were decidedly tlie longest; nevertheless, these 

 trees were speedily distanced in girth-increase by the other 

 species, and two-thirds of their increment was delayed till the 

 second half of the season. 



Interesting questions arise from the facts brought forward 

 in this paper. ' For example, — Why should growth be dis- 

 tributed over the months so variously in different species, 

 some effecting the largest part of their increase in a single 

 month, while in others it is pretty equally distributed over 

 two, three, or even four months ? Why should the maximum 

 growth in different species occur at such various periods as 

 June, July, and August? Why is it that some species complete 

 by far the greater part of their growth by the end of June, 

 before the real heat of summer has begun ? The explanation 

 cannot be found in atmospheric influences or in the nature 

 of the soil, as all the species are similarly circumstanced in 

 these respects. Possibly a difference in the depth of roots 

 below the surface may have some influence, the roots of 

 some species being reached earlier than others by the 

 gi-adually descending heat of spring and summer. Struc- 

 tural dilTerences may also have something to do with it; and 

 it is perhaps not an extravagant supposition that introduced 

 tre(;s may still bear the impress of the laws of growth which 

 regulated their ancestors in climates different from our own. 



