BOTANY. 111 
ise. The spore measurements, a delicate but necessary matter, 
have been well done. It may be added, that since the appearance 
of this work Mr. Cooke, in company with Mr. C. H. Peck of 
Albany, New York, has been engaged in the study of the Erysiphei 
of the United States, and has already published several papers 
which might well accompany the hand-book to the study table of 
any. American botanist.— E. C. B 
BOTAN Zz: 
Second Growrtus IN Trees.— A matter which has not received 
the attention which perhaps it deserves is the growth of trees 
twice or more during the same season. Some, like the horse 
chestnut, make but a single grow th, when the upper leaves are 
reduced to perfect bud scales; and although there is, probably, 
a growth of the embryonic parts of the next year’s leaves and 
flowers beneath these scales for sometime afterwards, to all 
appearance growth ceases for the season. Others, as in the 
Norway and sycamore maples, gradually decrease in the size of 
their leaves as midsummer approaches; the internodes occupy 
less and less space, but before finally taking on the condition of 
a terminal bud a new growth commences, the leaves grow larger, 
and before the final fall resting comes, they have nearly reached 
the size of those of the early summer time. The English oak 
almost always makes two of these growths, and sometimes 
three, and this is also the case with Pinus mitis, P. Banksiana, 
P. inops, P. pungens, and sometimes but not so frequently in P. 
rigida and P. Teda. I think it likely that in most trees which 
make a continuous growth through the summer season there 
is more or less of this growth rest, and successive reaction. In 
the apple tree, and the Carolina and cottonwood poplars, this ap- 
proach to rest about midsummer is very plainly seen by a short- 
ening of the internodes; after this they again widen, and in the 
case of these two, the leaves of the second growth are much larger- 
X and more vigorous in every respect than those of the first cycle or 
- wave of growth. I have often set myself to the study of the — 
causes of this varying growth force, without feeling satisfied that — 
I could comprehend them clearly. In some way it would seem to 
be dependent on the powers of nutrition, as in the apple and many 
other trees it is only the most vigorous shoots which make a re- 
