303 
Marsh, and its Relations to Evaporation, &c. 
The days on which observations were made at Wicken included 
a considerable variety of weather. Almost the only kind lacking was 
a really strong gale. But gales during the summer months are infrequent 
in the Fen country . 1 
It would seem, then, that the results obtained indicate fairly closely the 
normal range of evaporation under varying atmospheric conditions. Of 
course, even greater evaporation would probably occur on exceptional days 
in other summers. But in a climate such as ours the plants would only 
rarely be called upon, during the summer months, to endure much more 
severe transpiration conditions than on some of the days when the above 
records were made. In any case, there would still be great differences 
of evaporation in the different strata of the vegetation. 
The Mutual Protection of Shoots. 
The action of air-currents in increasing evaporation has been discussed 
above ; but the general relations of the vegetation to wind may be con- 
sidered a little more fully. There can be no doubt that wind is an ecological 
factor of the greatest importance. This point has been emphasized by 
many authors ; more especially with regard to the effect of wind on 
tree-life. 
The action of wind in increasing transpiration has been proved by 
Wiesner , 2 Livingston , 3 and others. 
Hansen 4 has shown that wind frequently causes considerable injury to 
leaves. According to him, the withering of leaves at the apices or edges, 
which is so commonly seen, is due to this cause. It is important to note 
that Hansen’s experiments prove that a strong wind is not necessary to 
cause this injury, provided that the wind is allowed to blow through the 
plant . 5 In another paper Hansen 6 affirms that all plants are sensitive 
to the drying action of wind. 
Again, Hansen 7 correlates the great prevalence of plants of low 
growth in the East Frisian Islands with the strong winds which regularly 
occur there. 
Kihlman , 8 Warming , 9 Schimper , 10 and others, have discussed the 
influence of strong winds in determining the configuration of trees and 
shrubs. 
Well-defined contours are characteristic of many plants which grow 
either in very windy localities, or in general under conditions which greatly 
favour transpiration. Examples are the dune-like trees on our sea-coasts ; 
1 Miller and Skertchly (’78), p. 284. 2 Wiesner (’88), pp. 182-214. 
3 Livingston (’06), p. 30. 4 Hansen(’04), pp. 38 et seq. 
5 Hansen (1. c., pp. 33 and 38) found that a continuous breeze, of a strength not exceeding 1-2 
(Beaufort scale), was sufficient to wither the edges of the leaves of young tobacco plants. 
6 Hansen (’01), p. 66. 7 Hansen, 1. c., pp. 26 et seq. 
8 Kihlman (’90), pp. 61 et seq. 9 Warming (’96), pp. 37 et seq, also (’02). 
10 Schimper (’03), pp. 76 and 347. Cf. also references given by these authors. 
