38 EXPLOITATION OF PLANTS 
intakes demand. With higher prices the position is 
altered, and, should there be a reasonable probability 
of their continuance, no doubt the reclaiming of salt 
marshes will once more receive attention. . 
In the past not a few of the reclamations, especially 
in estuaries and harbours, have been imprudently made 
with serious results to the navigation. The decayed 
ports of the north coast of Norfolk are outstanding 
examples. No operation is more tempting than to 
bank off the head of an estuary and to convert it into 
rich pasture or tillage. But in so doing the fact is too 
often lost sight of that the capacity of the estuary for 
storing tidal water is seriously impaired, and in par- 
ticular it is robbed of just that storage space which holds 
the water that flows away relatively late in the ebb, 
and has the greatest effect in scouring the channel at 
the outlet. Deprived of this natural means of clearing 
the mouth, silt gradually works up channel and raises 
the level of the bottom, with the inevitable consequence 
that navigation is seriously compromised. For the 
sake of a few hundreds or even thousands of acres of 
new land it is hardly worth while to destroy a port, 
for, after all, our maritime facilities must remain one of 
our greatest assets. 
Much less risk of silting up is incurred when the 
sides of an estuary are banked off by longitudinal works, 
whilst the scour of the ebb can be concentrated at 
the effective place by means of training walls. These 
operations, however, belong to the province of the 
maritime engineer rather than to that of the botanist. 
Ecological investigations show that the botanist has a 
field_of usefulness in such operations in speeding up 
