844 JOURNAL OF FORKSTKV 



disposing of the theory that acidity is required by fir. The difference 

 in rate between the neutral and acid cultures was greater in fir than in 

 spruce, indicating that, contrary to the common conception, spruce 

 withstands acid better than fir. Growth of both fir and spruce on the 

 mineral soil was slightly more rapid than on the raw humus, except 

 that toward the end of the season some of the spruces on the raw 

 humus began a second period of elongation which enabled them to pass 

 those on the mineral soil. Figure i shows graphically the growth of 

 spruce on each of the three soils and figure 2 shows the same for fir. 



The second period of elongation in spruce is a curious phenomenon 

 which, when better understood, may throw some light on the response 

 of the tree to the various influences surrounding it. Growth in length 

 became slow by July 10, and by August 10 the winter buds began to 

 form, indicating cessation of growth in length for the season. But by 

 August 20, after a rather warm ten days without rain, some of these 

 newly formed buds burst open and started to grow just as at the be- 

 ginning of the season. That soil as well as climate plays a part in this 

 phenomenon is indicated by the percentage of trees afifected on the 

 different soils. On the raw humus 38 per cent started a second growth 

 period ; on the mild humus 1 1 per cent, and on the mineral soil only 9 

 per cent. 



A similar second growth period has been noticed by NachtigalF^ in 

 4-year-old Norway spruce in Germany in the course of an experiment 

 similar to the one here described, except that the measurements were 

 made on trees in the forest. Curiously enough, the beginnings of 

 growth, the period of maximum rate, and the cessation of growth in 

 Germany closely parallel that on Mt. Desert Island, only being about 

 15 days later on Mt. Desert Island. 



The duration of the period of growth in length for the different 

 species is the reverse of what we would expect from the rate of growth 

 shown by stem analyses. The fir buds opened on June i and stopped 

 elongating on July 10, 40 days later; spruce and white pine began on 

 June 5 and did not stop till August 20, a period of 75 days, or nearly 

 twice as long as that of fir. Yet the fir is a faster-growing tree than 

 spruce. The explanation may be that the fir gets its new needles mnrc 

 quickly than spruce and then continues its diameter growth for the rest 

 of the season. Unquestionably, diameter growth continues long after 

 height growth has stopped. The shorter period of fir is probably cor- 

 related with the more northerly range of this tree as compared with 

 spruce. 



See note 8 for citation. 



