GIANT BAMBOOS. 
261 
was nearly constant,and we are bound to suppose the conditions 
of moisture to have been so also, but we are not told to what 
conditions of atmospheric moisture the plants had previously 
been exposed. Is there not a possibility that an after effect 
from previous alternations of a drier atmosphere by day and 
a moister by night might become apparent in this manner ? 
This seems to me to be more likely than that there should 
be inheritance of the effect of still earlier alternations of 
darkness and light. 
Sachs regarded this experiment as showing that plants 
normally exhibit a daily periodicity quite apart from changes 
of light and temperature. But the effect of changes of 
moisture must also be excluded before this periodicity can 
be called spontaneous; and it appears doubtful whether this 
has ever been done completely. 
Almost all the investigations which have been made in 
this direction have had for their object plants exposed to 
quite unnatural conditions. And recent experiments, for 
example those of Singer* and of Richterf upon the influence 
of the air of a laboratory upon the growth of plants, show 
very clearly how powerful an influence may be exerted upon 
the processes of growth by factors which have been probably 
very largely overlooked in the older experiments. It seems 
very desirable that careful records should be made of really 
normal growth in a number of different plants. 
The great importance of moisture for growth and the very 
regular occurrence of the change from drier air by day to 
moister air by night, the existence of which is a matter of 
common observation both in England and at Peradeniya, 
makes it highly probable that periodicity of growth may be 
found in other cases to be connected with periodic changes 
of moisture. 
Another function, the periodicity of which may show a 
like relationship, is that of root pressure. This has been 
* Berichte der dent. Bot. Ges. XXI., 3, p. 175,1903. 
t Berichte der dent. Bot. Ges. XXI.. 3, p. 180. 
8(10)04 (17) 
