28 BOTANICAL GAZETTE JANUARY 
Fifteen plants were grown in each condition. At the end of the 
experiment each had produced six to eight mature leaves. The 
leaves were measured as to length and breadth. An index was 
obtained by multiplying these two numbers together and averaging 
for each culture. Following are the indexes of leaf area thus derived: 
drained warm substratum 1268.3, drained cold 682.6, undrained 
warm 518.5, undrained cold 421.8. 
In the spring of 1904 the experiment with Rumex was repeated. 
The results correspond with those of the preceding year. The 
structure of the leaves, resulting in the several cultures, was investti- 
gated, and found to show marked variations (§6). Fig. 14 represents 
the cross-sections and average leaf areas produced (seventy-five 
leaves being measured in each case). When grown on a warm 
drained substratum, the leaves are large, and the cells are exceedingly 
loose and turgid. The epidermis is composed of large thin-walled 
’ cells, having a thin cuticle outside. The mesophyll consists of a 
single layer of palisade and three layers of spongy tissue. No resin 
bodies are present. The plants grown in the undrained substratum, 
whose temperature was reduced about 8° C. below that of the air, 
show marked xerophilous characters. THe leaf is reduced in area, 
increased in relative thickness, and the margins become revolute; 
the epidermal cells are smaller and outwardly. thick-walled; a well- 
marked cuticle is present; the mesophyll is very compact and made 
up of two or three layers of well-developed palisade cells and three — 
layers of spongy tissue; and in the epidermal cells and those adja- 
cent to the bundles there are marked accumulations of resinous 
bodies. 
For the purpose of comparison, a corresponding set of plants 
were grown on sand kept just sufficiently moist to allow the plants 
to live. As will be seen in fig. 14, the xerophily is not more marked 
than that of the undrained cold bog substratum. Fig. 15 shows the 
relative appearance of the plants produced by the different con- 
ditions. 
In the case of the plants grown in the undrained warm and the 
drained cold substrata, these same effects were noticeable, but to a 
less marked degree. That, in the case of the undrained cultures, 
. these effects are not due to the acidity of the bog water is shown by 
