112 BOTANY. 
newed start; but on the other hand I have seen two trees of 
English oak side by side together for about twenty years, one 
making mostly three of these growth cycles, and the other but 
two, and yet up to this time neither of these has gained any advan- 
tage in size over the other. Again, in the case of the horse chest- 
nut, if the leaves be picked off before the terminal bud is quite 
mature, it will make another growth the same season. In like 
manner if the leaves of most trees be taken off before the cycle 
of growth has been quite completed, most of the axillary buds, 
which otherwise would have remained dormant till the next year, 
will at once push into growth. If the leaves have to aid in the 
immediate nutrition of the axis with which they are connected, 
which I am sometimes led half to doubt, the check to nutrition by 
their loss,seems rather to aid more than full nutrition does in the 
secondary axial development. It is however certain that it is the 
most vigorous growths on any tree, or the most vigorous individ- 
uals, or even varieties, which make these repeated cycles. The 
common European ash rarely makes a second growth unless in a 
very vigorous condition. The variety heterophylla, which makes å 
longer, and a stouter growth, usually makes two ; but another vari- 
ety, known in gardens as Fraaxinus excelsior jaspidea, which has 
stouter branchlets than either, generally makes three growths. 
It would be very interesting to know exactly the relation be- 
tween nutrition and accelerated growth as exhibited in these suc- 
cessional waves. I have, in papers no doubt familiar to many of 
your readers, shown how varying powers of nutrition modify the 
_ form of leaves, and in other cases even regulate the production of 
the sexes; and it is by no means improbable that the same laws 
= will be found operative in the production of species itself; for 
frequently specific, perhaps one might say generic, differences are 
no greater, than are sometimes found in the varying growths on 
the same tree, or the differences between one sex and another. 
This is a well known fact, as genera of both plants and animals 
have not unfrequently been founded on specimens which were in 
time found to be but another sex of the same thing. 
_ A knowledge of these successive annual growths may aid our 
Diiis in systematic botany. As Mr. Gilman points out, in the 
American NarturaLIst Vol. vi, p. 684, in his note on the gray 
pine, Dr. Engelman divides our American pines according as the 
pedan is lateral or terminal. But = all these bine are 
