ECOLOGIC SUBTERRANEAN ANATOMY OF PLANTS 89 
the moist parts of the tropical region. The author does not regard these 
bulbs or tubers as reservoirs of starch or sugar, as is true of the similar or- 
gans of the Liliaceae and Iridaceae. Though they are structurally homol- 
ogous with these, physiologically they are reservoirs. The author has 
shown that Poa hulhosa on being cultivated in moist soil almost loses its 
bulbous character. The second group includes forms in which the bases 
of the culms and shoots are covered with at least three faded sheaths. 
These all inhabit dry localities. In those forms which prefer damp or shaded 
places there is usually one faded sheath present, and even that disappears 
soon. Straw tunics are distinguished from fiber tunics; in the former the 
sheath remains complete although faded, in the latter the sheath breaks 
up into fibers. The function of these tunics is regarded as that of water 
conservation. Holm has contributed various studies on the morphology of 
subterranean portions of plants. 
Gross Anatomy 
In the alluvial basin region the prairie plants under observation show a 
prominent development of thickened, elongated rootstocks. The majority 
of these plants are Gramineae, Cyperaceae, and Compositae, in which this 
feature is a systematic character. The Cyperaceae are seldom found on the 
highland, but the upland members of the Compositae and Gramineae, while 
they retain their rootstock characters, have abbreviated forms. The Gra- 
mineae especially show abbreviated subterranean parts in the form of hard 
bulbous or corm-like thickenings from which the roots radiate, or of short 
hard rootstocks. Panicum virgatum, which has a wide range of habitat, 
growing either on upland or lowland, has hard, radially branching, slender, 
scaly rootstocks which are shorter in the drier upland habitats. Spartina 
Michauxii, which grows on lowland or in moist upland ravines subject to 
drought, shows shorter rhizomes on the upland. The Solidagos which fre- 
quent the ridges have very abbreviated, hard, corm-like subterranean 
stems, while those which frequent moist habitats have longer rhizome-like 
structures. The genus Liatris has a species with short, sheathed corm which 
grows on the hilltops and a species with an elongated, fibrous-sheathed 
tuber on the moister slopes. Helianthus grosseserratus has a short, thick 
rootstock, while H. tuberosus has a long, slender-stemmed tuber. Silphium 
laciniatum is provided with a deep root. The Compositae are variable, 
having short tubers, elongated rhizomes, corm-like structures, or tap and 
fascicled roots, which enable them to thrive in a wide range of habitats and 
probably account for their great numbers and diversity of forms. Among 
the Leguminosae are Desmodium illinoense, Amorpha canescens, Lespedeza 
canadensis, Petalostemum purpureum, and P. albidum, which are upland 
plants with deep, tough roots, usually having long, thick tap roots and 
somewhat smaller lateral roots. These leguminous plants and others with 
