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REVIEWS. 
and others. The leaves of these plants are small, and the green stems 
often carry on the greater part of the work of transpiration and 
assimilation. The stems of such plants are provided with a thick 
epidermis and deeply-snnk stomata. On a very hot day and in a very 
exposed place, Cereus triqnetra lost by transpiration from 8 A.M to 6 
p.M. 0 01 gram per quadratdecimeter. Holtermann also carried out 
experiments which proved that the tobacco plant lost twice as much 
moisture at Jaffna as at Peradeniya, and that the transpiration in the 
drier districts of north Ceylon is considerably greater than in the 
moist climate in the south-west of the Island. He also states that 
though a change of external conditions did not lead to any great 
difference in the transpiration from Cyanotis zeylanica, yet other 
plants which had been transplanted into pots transpired more than 
those cultivated under natural conditions, and showed striking changes 
in the anatomy of their roots. 
H. W. 
Periodäcäty of Growth in Thickness of Stems 
in the Tropics. 
(Zur Periodicitat des Dickenwachsthums in den Tropen, von 
A. Ursprung, Botan. Zeit., Heft X., 1904.) 
The paper under review is an interesting contribution to our 
knowledge of the periodicity of plants in tropical areas and the 
relationship of foliar periodicity to anatomical differentiation. 
Ursprung regrets the absence of definite information regarding the 
periodic behaviour of most trees in the tropics, and points out the 
necessity for such knowledge before the zones of growth in the stem 
can be interpreted. 
In the introduction Ursprung points out that the differences 
between spring and autumn wood depend upon the periodic formation 
of certain types of cambial products, and suggests that the relationship 
of the latter to foliar periodicity requires special consideration. 
In discussing the origin of the periodicities of leaf activity he states 
that a knowledge of the climatic conditions which existed at the time of 
the origin of the species referred to would be valuable. He traces the 
foliar periodicity and zone formation in trees growing in uniform 
climates to internal forces, but allows that where the periodic climatic 
differences are great the external forces are of vital importance. 
A description of the characters of the rings of growth of several trees 
common in Ceylon is given, and the differences of these when the tree 
is grown in the relatively equable climate of Buitenzorg and unequal 
climate prevailing in East Java, are described. Every species dealt 
with provides material sufficient for a separate paper, but space 
prevents my giving more than a summary of Ursprung’s conclusions. 
