Marsh , and its Relations to Evaporation , &c. 307 
the physical conditions may be at a given moment, they are fairly uniform 
for the entire plant. 
On the other hand, both Cladium and Phragmites are, relatively speaking, 
plants of extremes. Their roots are fairly deeply placed in permanently 
wet soil, while their leaves reach levels where the effect of wind and the 
range of temperature and evaporation are at a maximum. Not only are 
the leaves themselves liable to frequent and sudden fluctuations of con- 
ditions, but the absorbing and transpiring organs will often be, at the same 
time, under widely differing conditions. But the problems of even these 
two plants are not the same, for while Cladium is evergreen, the aerial 
shoots of Phragmites are annual. 
In fact, it is scarcely going too far to assert that few of the species of 
plants forming the vegetation of a marsh have to face precisely the same 
set of physiological problems . 1 
It may be pointed out further, that in the case of such plants as 
Cladium , &c., the task of securing complete co-ordination between the 
functions of absorption, conduction, and transpiration, must be a com- 
plicated one. Several authors 2 have drawn attention to this point ; more 
especially with regard to the effect on transpiration, of warm air or strong 
winds, coupled with low soil temperatures. Such a combination often 
occurs on sunny days in winter or spring. 
But the converse simplification of the problem of transpiration, in the 
case of small plants, appears to have attracted less attention. Here all the 
various organs of the plant will be, at a given time, under fairly uniform 
conditions of temperature, &c. Schimper , 3 however, in one of his papers, 
referred to the wintering of delicately formed plants, such as fungi, algae, 
&c., and herbs like Stellaria media , &c. These, he said, behave like the 
soil, as far as temperature fluctuations are concerned, and so do not need 
any protection against transpiration. 
In our country, the contrast in winter time between delicate green 
seedlings, dwarf grasses, &c., on the one hand, and the tall bare trees 
or strongly xerophytic evergreen shrubs, on the other, is a striking one . 4 
The authors cited above have dwelt more particularly on the dangers 
of excessive transpiration in winter or spring. But though in our climate 
these dangers are perhaps the most serious, they are not the only ones. 
All the evidence adduced in this paper tends to show that even in summer 
time the atmospheric conditions may be unfavourably severe, as regards 
the most exposed shoots of the vegetation in question. Thus it is perhaps 
1 cf. Warming (’96), p. 119. 
2 e. g. Schimper (’90), pp. 647 et seq. Also Kihlman (’90), p. 107. 
3 Schimper, 1. c., p. 649. 
4 A good many authors have, of course, remarked on the shelter from wind, & c., afforded by a 
low habit of growth ; e. g. Meigen (’94), p. 408, Hansen (’01), &c. 
Y 
