THE ECOLOGIC FOLIAR ANATOMY OF SOME PLANTS OF A 
PRAIRIE PROVINCE IN CENTRAL IOWA 
Ada Hayden 
Introduction 
While exact records of environmental factors such as edaphic features, 
temperature, light, water, and biotic relationships are essential in the de- 
termination of the character of plant habitats, such data serve merely as an 
introduction to the investigation of the adaptation or equipment of plants 
for living in specific locations. While certain external characteristics, 
such as small or dissected leaves, are associated with sun plants, and broad 
leaves with shade plants, histological study reveals in greater detail any 
modifications of the normal type of tissues which are known to perform 
special activities. That the activities pertaining to the life processes of 
the plant are closely associated with its use of water is a well known phys- 
iological fact, so that not only the available water of the habitat but that 
which the plant actually uses or what passes through it in the transpiration 
stream is an important indicator of its toleration of conditions peculiar- to its 
particular habitat. Work has been done by Livingston, Bakke, Shreve, 
and others on the transpiration of plants, and Bakke (i) has proposed a 
classification of plants as xerophytes, mesophytes, or hydrophytes on the 
basis of transpiration, which it seems is a very exact indicator of the available 
water used. While indices of transpiration would no doubt be desirable in 
connection with a morphological study, and would probably throw some 
light on whether a special type of tissue were characteristic of a species 
because of reaction to habitat or because of ancestral influence, the obser- 
vations reported in this paper are confined to the morphological phase alone. 
Selection of Material 
Leaves and subterranean portions were chosen for examination since 
these organs are critical "indicators" of absorption and transpiration of 
water and therefore are more closely related to the regulation of the water 
supply than stems, which serve primarily as conductors. The plants 
selected were representative species of their habitats, i. e., those species 
which were facies, or prominent in frequency or as to their vegetative per- 
fection, for such plants may be regarded as instances of successful occupa- 
tion of their respective environments. 
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