PSORALEA TENUIFLORA AS A TUMBLE-WEED. 



By Leste^ F. Ward. 



IT is well known that the Psoraleas are often tumble-weeds, but 

 being perennials, they must differ in this respect from most other 

 tumble-weeds, which are annuals and blow up by the roots. 

 While operating in Southwestern Kansas during September 

 and October last, where the P. temiiflora is very common, I took par- 

 ticular notice of this point. Before leaving the field many of them 

 had begun to blow across the plains, and, besides good herbarium 

 specimens, I collected the basal portion of the stems of some of the 

 larger ones that had become detached, and I 

 observed that the point of separation was al- 

 ways very close to the ground and had a uni- 

 form character. There are several points near 

 the base where it looks as though there were 

 nodes, there being a slight elevation all round 

 the stem. It is at one of these, perhaps always 

 the lowest one, that the detachment takes place, 

 and in such a manner as to show a perfectly 

 even surface in the cross-section. The stems 

 have the appearance when lying on the ground 

 of having been neatly cut off by a fine saw, and 

 a closer inspection shows that the plane of sep- 

 aration is almost as smooth and even as if such 

 were the case In some cases there seems to be 

 a slight concavity on the distal side of this plane, 

 leaving a corresponding convexity on the prox- 

 imal or root portion. In other cases this is 

 scarcely apparent. 



It is obvious that the separation takes place 

 at a natural joint, and that this is a provision 



of nature expressly adapted to the function of distributing the seeds. 

 It is effected in such a way that the tissues along the plane of the 

 joint disintegrate at precisely the proper stage in the development of 

 the pods to secure the greatest degree of success in carrying the plant 

 to remote distances under the influence of the wind, and thus scat- 

 tering the seed broadcast over the plains. 



Whether more than one joint on the same plant has this function 

 could only be proved by further investigation; certainly there are 

 always two that have the same general appearance, and sometimes a 

 third, and it seems probable that these are developed to increase the 

 certainty, so that if for any reason one of them fails another will suc- 

 ceed in dismembering the plant. 



