92 
sphere, or after smearing the injured surface with vaseline, 
The paper on Contact Irritability leaves openings for further 
research in two directions at least. Thus it is still uncertain 
whether a strain set up in a hook-tendril of Strychnos, without 
any contact stimulus in the strict sense of the term being 
applied, is able to act as a stimulus to increased cambial activity. 
The manner in which this problem can be attacked has already 
been described (1. c. p. 215). Similarly many tropical shrubby 
climbers possess tendrils which become permanent attaching 
organs and which, like hooks, may persist for 2, 3 or more 
years. In all such cases the tendril undergoes a marked se- 
condary increase in thickness due to the renewed activity of the 
wood cambium induced by the stimuli of pressure, contact and 
mechanical strain, and it is not as yet in all cases quite certain 
what are the precise parts played by these different stimuli in 
producing the observed end result. (See 1. ¢. p. 215, 219 ete.). 
A problem of very different character to the above but 
nevertheless an extremely interesting one is that which is 
concerned with the active processes of decomposition and dis- 
integration which organic material undergoes in the tropics. 
In spite of the marked vegetative activity which characterizes 
the plants of a moist tropical climate such as that of Java, 
less accumulation of dead organic material takes place even 
in the deepest tropical forest than is to found on the floor 
of any European pine wood of moderate age. This is due to® 
variety of causes, such as the wealth of insects, especially 
ants, which prey upon dead wood, bark, etc., and to the fact 
that a warm moist climate is extremely favourable to the 
rapid growth and development of saprophytic fungi. The more 
rapid decomposition of the bodies of animals and of the soft 
parts of plants is clearly mainly due to the disintegratory 
action of putrefactive bacteria and the interesting point ab 
Once arises as to whether the more rapid decomposition is due 
to the action of specific bacteria peculiar to the tropics. It 
true that the commoner bacteria appear to be world wide ™ 
distribution, and my own observations have shewn that this 
