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 incfiica 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. 



io6 Wright, H. Foliar periodicity of endemic and indigenous trees in 

 Ceylon. Ann. Roy. Bot. Card. Peradeniya 2:415-516. 1905. 



