88 
ADA HAYDEN 
Methods 
The material was stored in 50% alcohol, and after free-hand cutting the 
sections were stained with a solution of water-soluble safranin, followed by 
haematoxylin, cleared in cedar oil and clove oil, and mounted in Canada 
balsam. The drawings of the subterranean structures were not made to a 
single scale because the large size of some of them made this impracticable, 
and also because of the variability in size, which makes the comparison of 
the size of the roots and stems of species less important than the relative 
proportion occupied by the tissues of the roots compared. 
• 
Historical 
Some progress has recently been made in classifying subterranean or- 
gans; among the valuable contributions are those of Cannon (2), Harsh- 
berger (11), Holm (13), Yapp (18), Dauphine (6), Constantin, Jodin (15), 
and Maxwell (16). 
Maxwell (16) reviews the history of the histological study of roots, which 
before 1865 were studied as masses of tissues and after this period with ref- 
erence more directly to the origin of organs. 
According to Cannon (2), the work of Rimbach, Biisgin, and Frieden- 
feldt as reviewed by Von Alter (Wurzelstudien, Bot. Zeit. 67: 175. 1909) 
is important because their researches indicate that the root systems of 
flowering plants may be divided into two groups according to the character 
of the terminal roots; they are either intensive or extensive. Intensive root 
systems have fine terminal roots ; they are richly branched and occupy small 
soil volume. Extensive root systems have coarse ultimate roots, are not 
richly branched, and occupy a relatively large soil volume. Cannon de- 
scribes three main types of root systems found in the desert plants of the 
southwestern United States: {a) Root systems which extend horizontally 
from the main axis and lie for their whole course near the surface of the 
ground, ih) Root systems which are characterized by a strongly developed 
tap root going down directly to a depth determined in part by the character 
of the soil, in part by the penetration of the rains, and in part by the char- 
acter of the root itself, {c) Roots that not only reach widely but pene- 
trate fairly deeply. When the root is of an obligate type the distribution 
of the species is much restricted, but when it undergoes modification with 
changed environment the distribution of the species is much less confined. 
Yapp (18) and Scherff (17), in their marsh studies, note the stratifica- 
tion of subterranean systems as well as the aerial portions of different spe- 
cies. 
Holm (13) reviews a paper of Hackel (10) on the peculiarities of the 
grasses of dry climates, among which he distinguishes {a) tuberous and 
bulbous grasses and (b) tunic grasses. The tuberous and bulbous forms occur 
only in countries with periodic dry seasons. None have been observed in 
