336 Meyen's Report for 1839 on Physiological Botany. 



the case of marks made on those trees in forests which are 

 destined to be sold. 



M. C. van Hall* has laid before the Academy of Sciences of 

 Amsterdam a series of observations on the increase of trees in 

 thickness, by which it is clearly shown which trees thicken 

 slower or faster, and what is the proportion of increase in 

 different ages, different years, and even in the several months. 

 An oak stem which in 1826 had a circumference of 140 mil- 

 limetres-]-, during ten years increased yearly on the average 

 37 mill, in circumference ; an oak of 555 mill, increased during 

 ten years 307 mill., or yearly 30 t 7 q mill. ; and another of 1 792 

 mill, in circumference increased yearly only 12^ mill. An elm 

 of 170 mill, increased yearly on the average 36 t 3 q mill.; an- 

 other of 190 mill. 32| ; and one of 1155 mill, only 20f mill. 

 A willow (Salix alba) of a circumference of 191 mill, increased 

 47^ mill., and one of 1130 nearly as much. The Canadian 

 poplar (Populus monilifera), in circumference 620 mill., in- 

 creased yearly as much as 81 mill.; and one of 1645 mill, 

 even 91 \ mill. Birch and maple, on the contrary, increased 

 even when young only about 10 or 12 mill. Pinus Abies, Tilia 

 europaea, Juglans regia, and JEsculus Hippocastanum were 

 measured in the same manner. Moreover, seven different 

 kinds of trees were measured for five years during the 

 summer monthly, and these measurements in particular 

 have given good results. It appears, first of all, that the 

 increase in the five years w r as not always the same, and that 

 no determinate increase or decrease therein, according to the 

 age, could be observed. The increase of the circumference 

 varied very much in the different months of the several years, 

 which is evidently to be referred to the weather. We will here 

 give only one of the tables in order to prove the above state- 

 ments. A stem of Ulmus campestris measured in February 

 1834 265 millimetres, and increased in millimetres 



M. van Hall remarks, that by the observations, the opinion 

 of Agardh, that trees increase in length in the first part of 

 the summer and in breadth in the latter part, is proved to be 

 unfounded ; and that they also show that the circumference 

 of stems is not altered during the six winter months. 



[To be continued.] 



* Waarnemingen over de Toeneming der Boomen in Dikte. — Tijdscbrift 

 voor Natuurl. Geschied. en Phys. 1839, vi. p. 207. 

 f The millimetre is -03937 of an English inch. 



