ORIENTATION OF SECONDARY TERRESTRIAL ROOTS 409 
had emerged.^ Figure i shows camera drawings of two such roots. 
Of these roots, the upper one had grown 2.2 cm. after leaving the soil 
(the surface of which is represented by the horizontal Hnes) and the 
lower one 3.2 cm. 
Sachs^ is the first author who reported any comparative observa- 
tions of the behavior relative to gravity of secondary roots in different 
media. His principal observations were, 1st, that the limiting angle 
(Grenzwinkel) of secondary roots growing in air was greater than that 
of roots growing in water and greater in roots growing in the latter 
medium than in the case of secondary roots growing in earth, and, 2d, 
that, in aii, the relatively acute curvatures resulting from displace- 
ment of the roots upward from the limiting angle or from sabjecting 
them to a stimulus greater than gravity, by means of the centrifuge, 
were later flattened. Sachs employed principally seedlings of Vicia 
faba. Relative to the first of Sachs' observations, stated above, 
Czapek^ reported that wetting of relatively dry sawdust cultures 
resulted in an increase, rather than a decrease, in the limiting angle 
of secondary roots growing in the sawdust. This result was just the 
opposite of what Sachs had reported when dry soil cultures were 
abundantly wetted. Both Czapek and Sachs stated however that the 
behavior of roots under the conditions mentioned was very inconstant. 
Sachs's own statement^ that secondary roots in air which are not 
frequently wetted lose their ability to bend downward suggests that 
the roots which showed a smaller limiting angle in air than in water 
may have behaved thus on account of too low humidity of the air 
surrounding them. 
My own experiments with Vicia faba var. equina and var. major 
and with Lupinus albus and Pisum sativum disclosed a striking parallel 
in the behavior of primary roots and secondary roots of the first order. 
Vicia faba was used for most of the experiments because of the large 
number of secondary roots which it produces and the great vigor of 
growth which they display. (There are usually five rows of secondary 
roots in the case of Vicia faba, two rows in the case of Lupinus albus 
and three in the case of Pisum sativum.) The media used were air, 
3 L. c, 609 ff. 
^Czapek, Ueber die Richtungsursachen der Seitenwurzeln und einiger anderer 
plagiotroper Pflanzentheile. Sitzungsb. Akad. Wiss. Math. Naturw. (Wien) 104: 
I Abt: 1253. 1895. 
^ Sachs. 1. c, p. 609. 
