Grossenbacher—Radial Growth in Trees. 
51 
in February or March. All stages of bud and leaf are said 
usually to occur in these trees. 
An experiment similar to that performed by Dingier had pre¬ 
viously been made by Wright 105 in Ceylon. He lopped trees of 
Mangifera indica and Terminalia Catappa in May and new 
leaves developed from July to September, with the result that 
no new leaves were produced on these trees in February and 
March when others of those species developed new crops of 
leaves. Some of the plants develop new leaves once or twice and 
others several times annually, and immature leaves may be found 
during every month of the year. Only a comparatively small 
percentage of the Ceylon trees are said to be deciduous. Some 
rapidly growing species were found to become defoliated at the 
end of the first year and others at the end of the second; while 
the more slowly growing ones may vegetate as evergreens until 
the close of the fifth or sixth year before losing their leaves. 
Usually, after a tree has once lost its leaves it loses them annually 
but some species are deciduous only in youth and become ever¬ 
green later. Some of the so-called evergreen trees are said to 
also lose all the leaves in occasional years before the new crop ap¬ 
pears. In some species periods of sparse foliation occur two or 
three times per year and in others the foliage is more copious 
on alternate years. It is held that the absence of any very 
marked periodicity in the environment permits some plants to 
follow their inherent periodicity of growth, while the annual 
variation in the transpiration rate and atmospheric moisture are 
thought to be the cause of the deciduous habit of others. 
These observations on foliar periodicity by Dingier, Wright 
and others seem to show that Dingier may be correct in his con¬ 
tention that leaf-fall is more dependent upon the normal dura¬ 
tion of life of the leaves than upon the environment. However, 
if that should prove to be a fact, it would necessarily follow that 
certain plants are deciduous not because of the leaf-fall but on 
account of the failure of a new crop of leaves to develop before 
the old ones drop. Such a view centers attention upon the causes 
inhibiting growth rather than upon the causes of leaf-fall in the 
study of periodicity, a method of attack adopted by Klebs in the 
paper cited above. 
106 Wright, H. Foliar periodicity of endemic and indigenous trees in 
Ceylon. Ann. Roy. Bot. Gard. Peradeniya 2:415-516. 1905. 
