STEMS, LEAVES, AND BUDS. 
53 
In Froriep’s Neuen Notizen, vol. xiv. p. 242, we find Von 
Hall’s Observations on the Increase of Trees in Thickness, 
read at the Royal Institution of Sciences of the Netherlands, 
&c., first class. The observations were made on the oak, 
willow tree (Salioo alba), Canadian poplar {Populus monili- 
fera), horse chestnut, birch, maple {Acer pseudo-Platanus), 
lime tree, fir tree {Pinus abies), and the wallnut tree. I will 
pass over these observations, as the relative growth of these 
trees depends much on the soil in which they grow, and the 
observations only refer to trees in the same locality. The 
author has frequently made the observation, that the increase 
of growth, in point of thickness, is considerably lessened by 
the tearing off* of the foliage, and the taking olF of many and 
strong boughs, which is opposed to the opinion of the advo- 
cates of pruning trees. The author further instituted investi- 
gations on the increase of thickness in dififerent months of the 
year. The tables on this point exhibit a proof, that the 
growth of trees in Holland is very variable, which no doubt is 
owing to the weather and temperature of that country. As a 
general rule, however, we learn, that the months of June and 
July are those in which the trees increase most in thickness, 
for the growth in these two months, in most cases, exceeded 
that of all the other months put together. The author did 
not observe a suspension of growth of trees from the latter 
half of June to the middle of August, as recorded by Duhamel 
for France ; this is unquestionably owing to the fact, that 
there is no dry season in the summer in Holland. The 
opinion of Agardh is unfounded, that trees grow more in 
length in the first part of the summer, and more in thickness 
in the latter part of it. Trees do not increase in. thickness 
during the winter months ; the buds, however, thicken. The 
branches of birch, maple, and other similar trees, are seen 
to be filled with rising watery juices in March and April, if 
the weather is mild, which cannot be perceived so much, or 
not at all, as soon as the weather becomes warmer. These 
juices, however, have no influence whatever upon the increase 
of thickness in a tree. The superabundance of this rising 
juice decreases as soon as the leaves have perfectly shot forth. 
