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 investi- 

 gated, and found to show marked variations (56). 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 



