Mat 1891.] BOTANICAL SOCIETY OF EDINBURGH. 119 



further observations are desirable on this point. Should the 

 result be confirmed, it would indicate that the use of stored 

 materials and the functions of the roots, and possibly of 

 the bark, may suffice for girth-increase without the leaf 

 being called into play. 



Correlation of Girth-Increase and Meteorological 

 Conditions. 



The length to which this paper has already run forbids me 

 from entering fully on the very difficult and complex sub- 

 ject of correlation of girth-increase with the weather in the 

 three years, but the broad fact may be pointed out that a 

 marked retardation occurred alike in the two summers of 

 1886 and 1890, which were unusually cold and wet, and in 

 the summer of 1889, which was unusually warm and dry. 

 There seems little reason to doubt, therefore, that the 

 phenomenon is a constant one. 



In 1890 I endeavoured to ascertain the relation between 

 weekly girth-increase and meteorological conditions, which I 

 was enabled to do by the recent introduction of strictly 

 scientific meteorological observations at the Garden. The 

 results are given in Table VII., but I do not venture to 

 analyse them at j^resent. A study of the kind is eminently 

 difficult and complex, from the number and variety of the 

 points which have to be considered, some of which may be 

 here pointed out. First, as to temperature alone, the 

 effects of low or high average maxima and minima, and of 

 extreme high or low temperatures. Secondly, as to rainfall 

 alone : not only its amount in any week, but whether it falls 

 at the beginning or end of the week, and whether it falls 

 after a course of dry or rainy weather. Thirdly, the effect 

 of sunshine and cloud. Fourthly, the effects of the above in 

 the very various combinations which may occur. Fifthly, 

 whether the effects of the various meteorological conditions 

 are immediate, or are delayed, and if so, for how long. 

 Sixthly, the relation of these complex phenomena to bodies 

 which follow certain as yet undetermined laws of growth, 

 independent of weather, although no doubt modified by it, 

 including the spring rise and autumn decline, but also 

 the intermediate retardation, possibly in all trees, and the 

 actual cessation of Q'irth-increase in some. 



