groups, each showing adaptive arrangements to fit it for its place in 

 nature. 



1. Water-loving plants, or those plants which live either wholly 



or partly in water, or else grow in very wet soil, where the 

 water percentage is 80 or above. This is an extreme form of 

 vegetation, and the number of species of plants in this class 

 in Indiana is relatively small. Technically such plants are 

 known as Hydrophytes. 



2. Dry soil or desert plants, at the opposite extreme from the 



water-loving plants. These plants grow in dry soil and atmos- 

 phere, the water content of the soil being below 10 per cent, 

 at its minimum. Such plants are known as Xerophytes. 



3. Intermediate plants, or those adapted to medium conditions of 



moisture in air and soil. Such plants are known as Mesophytes, 

 and constitute the larger portion of our native flora. 



While these differing soil conditions modify the structure of the en- 

 tire plant, we wish at this time to consider only their effect upon the 

 leaf. It is plain that when a plant lives in an extremely dry soil, that 

 the water lost 1jy transpiration can be replaced with extreme diffi- 

 culty, and that if no cheek were placed upon transpiration the avail- 

 able water in the soil would soon be exhausted and the plant would die. 

 On the other hand, when plants live in the water or in a soil rich in 

 water, the losses from transpiration, however great, can be easily re- 

 placed. As the foliage leaf is the chief organ of transpiration, the 

 most evident adaptations to control the process occur in it. 



Let us consider in what ways transpiration may be checked, and then 

 see if by an application of these facts, the foliage leaf will not tell to us 

 the story of the water capacity of the soil. 



1. Transpiration may be checked by reducing the size of the foliage 

 leaf. Much less water will be evaporated in a given time from a vessel 

 with ten square inches of exposed surface than from one with a sur- 

 face exposure of one hundred square inches. So, much less transpira- 

 tion will take place from a small leaf than from a large one. Think of 

 the leaves of the waterlily, of the splatter dock, of the skunk cabbage, 

 indeed of any water or marsh plant with which you are familiar, and 

 compare them as to size, with leaves of the golden rods or the mullein 

 or any familiar plant living in a dry soil. You will see at once a 

 marked contrast. In tropical regions where water is abundant both in 

 soil and air, the foliage leaves are very large, but as we come into the 

 temperate regions the leaves are reduced in size until finally in desert 

 or arctic regions they are so reduced that they almost lose the sem- 

 blance of foliage leaves. 



