84 
we have a right to. So for instance we have some data 
for the rain at Frankfort, which is not far from the place 
of our Rhine wood. Now the comparison here led to 
the result that spring- and summer-rain, have but an in- 
significant influence, whereas winter-rain shows some, 
though not very appreciable influence. In fact we already 
drew attention to the fact that the influence of rain must 
not be the same for all trees. It is evident that in a 
more complete study than the present can pretend to be, 
we ought to try to obtain complete data of the soil and 
situation of each tree we use for our purpose. Mean- 
while in many cases, having once found a tree which 
can be proved to have been sensitive to rain during, 
say, the last 20 years, as it has not changed place since 
its birth, if there seems to be little possibility of a fun- 
damental change in the watersupply, it can be used as 
a rough sort of raingauge for all the preceding years of 
its life, which may be centuries. 
IV. In many cases, perhaps in all, increased tree- 
growth is not caused by the greater quantity of rain 
directly, but indirectly through he greater height of the 
subsoil water. 
Proof. This is proved by a case which at first puzzled 
me very much. Whereas, as you have seen, there is a 
striking parallelism between the growth in the forests of 
the Main and those of the Moselle, there is a forest 
between the two, part of the Odenwald !), where the 
parallelism is no doubt still well recognisable, but where 
it still is far less. 
Ï collected my tree-sections near a place called Bürstadt. 
My difficulty was later on removed by a report in the 
papers, of an inundation of the Rhine, which caused the 
!l) Locally the forest is called the Lorscher Wald but I understand 
that it is an outlying part of the Odenwald. 
