68 
Ohio Naturalist. 
[Vol. 1, No. 5 
Fig 2 Plant of P floribund, showing a partof 
the deep taproot. 
The perennial tumbleweeds 
are especially interesting be- 
cause of the way in which they 
are separated from the under- 
ground parts. Among the pe- 
rennial forms Psoralea flori- 
bunda is one of the most 
typical. It is a longlived, 
perennial crown-former with a 
very deep root which may be 
several inches in diameter. 
From the short terminal stem 
of this root a number of aerial 
branches are developed annu- 
ally. These branches take on a 
more or less globose or balloon- 
shaped form. At the base of 
each aerial stem a number of 
special joints are formed in 
which transverse cleavage 
regions are gradually devel- 
oped, and when the seed is 
ripe the whole crown breaks off at these 
joints with remarkable ease. This is a pe- 
culiar case of the development of a self- 
pruning process in the stem for a very special 
purpose. 
Psoralea argophylla also develops perfect 
joints but fewer shoots usually make up the 
crown and it is therefore less conspicuous 
than P. floribunda. Psoralea esculenta is also 
a tumbleweed but the writer has not made 
an examination of the way in which it sep- 
arates from the thick, tuberous, perennial root. 
Psoralea floribunda is very abundant in 
north-central Kansas where the writer has 
seen great masses heaped up against hedge- 
rows and wire fences. These plants show a 
most remarkable responsive adaption to an 
environment of very definite conditions. 
They have developed nearly every character 
possible in harmony with the dry and windy 
plains of the west and may be regarded as 
ideal prairie plants. 
Fig. 3. (a) Base of a stem of 
P. floribunda with two cleav- 
age joints. (b) Base of stem 
showing cleavage surface. 
