334 BOTANICAL GAZETTE [APRIL 
of the soil water, and abandons the hypothesis that leaf-fall is due to an excess 
of stored food checking the activity of the leaf by preventing the removal of 
the products of photosynthesis. He finds the final cause of leaf-removal and 
leaf-renewal in the inherited, internal, unknown attributes of the protoplasm. 
He confesses that all his efforts to arrive at any explanation of these internal 
causes have been fruitless. External factors modify the action of these 
primary causes, but in a comparatively uniform climate like that of Java the 
modification is slight. 
VOLKENS also reviews the work of Wricut® and others upon deciduous 
trees, and that of SmirH™ which affords some data for certain ce species 
in Ceylon, and finds them in accord with his own observat 
n attempts to interrupt the regularity of leaf-fall, rican? in Ceylon and 
K1esBs® in Java removed all the leaves from individuals of various species a 
few months before their regular time of shedding, and obtained a prompt 
renewal of the foliage and its persistence throughout the period in which they 
were usually leafless. DINGLER sees in this a proof of the efficiency of the 
inner Cause in disregarding external conditions, while KLEBs, on the contrary, 
regards it as a response to external factors proving that a rest period is not 
required. Both these investigators have studied the behavior of deciduous 
European trees.in the tropics, DINGLER™ at a mountain station in Ceylon, and 
Kiess at Tjibodas, Java, and found the usual European habit largely 
abandoned, new foliage and flowers being often produced twice in the year, 
while many species never became entirely leafless. Several resembled tropical 
species in having at one and the same time branches in full foliage, with bursting 
buds and in leafless condition, respectively. From these and many other experi- 
mental studies KLEBs reaches the general conclusion that periodicity of plant 
life is conditioned by periodicity of external factors. 
n a more recent paper’ Kreps takes exception to VOLKENS’ statement 
that tropical vegetation in Java is mainly periodic, claiming that when all the 
constituents of the forests about Buitenzorg and Tjibodas are considered, there 
© Wricut, H., Foliar periodicity of Ee and indigenous trees in Ceylon. 
Ann. Roy. Bot. Cand Peradeniya 2:415-516. 
™ SmitH, A. M., On the internal coe of leaves in tropical insolation; also 
observations on the periodicity of the appearance of young colored leaves of tree 
growing in Peradeniya. Ann. Roy. Gard. Peradeniya 4:229-298. 1909. 
12 DINGLER, H., Versuche iiber die eee Soniye Holzgewiichse in den 
Tropen. Sitz. = Bay. Akad. Wiss. Miinchen. pp. IQII 
13 KLEBS, , Uber die pntionny in der aie die Pflanzen. Sitz. 
Anes par Wiss. Abh. 23 
r, H., Uber ea a sommergiinen Baume Mitteleuropas in 
iS cnokee poles Sitz. K. Bay. Akad. Wiss. Miinchen. pp. 217-247. 1911. 
1s Kress, G., Uber die periodischen Erscheinungen tropischer Pflanzen. Biol. 
Centralbl. ae IgI2. 
