44 THE AMERICAN BOTANIST. 



Seed Dispersal in Cassia. — The great pea family {Le- 

 giiminosae) has evolved numerous devices for the distribution 

 of its seeds. The tick-trefoils' (Dcsmodiuin) have a trait, so 

 common among the composites, of catching into the clothing 

 of animals for transportation, and various locusts (Robinia), 

 while not able to produce samaras have, nevertheless, pro- 

 duced winged fruits, for the pods split open and each half 

 blows away with its quota of seeds clinging to it. Fleshy 

 fruits, in the ordinary sense, are rare, but there are not a few 

 species in which a part of the pod is made edible to the delec- 

 tation of some mammal and the consequent distribution of its 

 seeds. The great majority of the family appear to depend up- 

 on the splitting of the pod to sufficiently scatter the seeds. 

 In some this splitting is a tame affair and the seeds lazily 

 tumble out on the ground, but in others the pods split with a 

 sharp snap and jerk the seeds for some distance. This is 

 true of partridge pea {Cassia dianiaccrista) which is able to 

 throw its seeds several feet by this means. The pods are so 

 constructed that as they dry an unequal tension is produced 

 and when this reaches the breaking point, away go the seeds. 

 The force of the discharge is increased by the twisting of the 

 pod which thus forms a veritable catapult. 



Plants and Sterile Soil. — It is apparent that botanists, 

 have not yet got to the bottom of the great question why cer- 

 tain plants grow in sterile soils. It is assumed, with pretty 

 good reason, that some plants have taken up their abode in 

 such soils because at least one phase of the struggle for exist- 

 ence is less intense. Although the cactus has to provide for 

 a drouth and resist evaporation, as well as protect its supply 

 of moisture from thirsty animals it does not haAC to compete 

 with grasses, and burdocks and many another plant that would 

 crowd it in more fertile soils. There are other plants, how- 

 ever, that seem to prefer the barrens and when removed to- 



