ECOLOGIC SUBTERRANEAN ANATOMY OF PLANTS 
103 
relative proportion of parenchyma, though in the plants of the drier habi- 
tats it was present in very slight degree. Mechanical tissue was prominent 
in most of the plants with large aerial portions, and usually absent in the 
low-growing plants with the exception of HeHanthus which seems to be a 
non-conformist in both leaf and stem characters and lives by a code of its 
own. The tracheae were also variable in size and number. In this small 
group of plants no correlation could be seen between the number of tracheae 
and the number of leaves. The presence of thick-walled cells not only 
serves as a reinforcing character but no doubt tends to preserve turgor and 
to protect water-conducting tissues against loss of water. 
Summary 
A study of the minute anatomy of subterranean organs of prairie plants 
shows: 
(1) There is a tendency to the production of prominent mechanical 
tissue in plants of dry habitats and reduction of parenchymatous tissue. 
(2) In moist habitats the proportion of parenchymatous tissue is prom- 
inent. Aerenchyma is abundant in swamp plants. 
(3) The vascular tissue is variable in quantity, seemingly more or less 
subject to systematic variation. 
The subterranean stem is predominant as an equivalent of the primary 
root, especially in moist lowland regions. It is more efficient than the root 
in propagation. Primary roots which show secondary thickening resemble 
stems in their concentric manner of expansion. The stem has an area of 
pith which serves as a reservoir for water and hence increases its efficiency 
for radial distribution. 
I wish to acknowledge the helpful comment of Dr. L. H. Pammel, Dr. 
J. N. Martin, and Miss Charlotte M. King in the preparation of this paper. 
Iowa State College, 
Ames, Iowa 
LITERATURE CITED 
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