68 



Ohio Naturalist. 



[Vol. 1, No. 5 



Fig 2 Plant of P floribund, showing a partof 

 the deep taproot. 



The perennial tunibleweeds 

 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 

 whicii transverse cleavage 

 regions are graduallj'^ 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 

 l^urpose. 



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 

 rhost 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. 



