172 MINNESOTA BOTANICAL STUDIES. 



gun may result from the overcoming of the resistance of the 

 restraining layer at the muzzle, or this event may be precipi- 

 tated by any force from the outside which would result in the 

 disturbance of the scission layer. One may stand under a pine 

 tree on a quiet morning and hear the sharp click accompanying 

 the expulsion of the seed from the berries at irregular intervals. 

 If the branches are jarred or shaken, however, the irregular ex- 

 plosions give way to fusillades by which nearly all of the berries 

 on a plant will be set in action at once. 



The expulsion of the seed occurs as soon as the berry has 

 broken loose from the stalk, and as these berries were originally 

 in all positions the seeds are sent out in all directions. The 

 mucilage adhering to the seed causes its attachment to the 

 branches or other bodies it may strike. In this 

 manner dissemination is effected throughout a 



O 



cylindrical space about seven meters in diame- 

 ter and extending downward to the ground. 

 The only localities which offer suitable condi- 

 tions for the germination and growth of the 

 seeds, however, are the tips of branches or the 

 shoots of young trees underneath. It is to be 

 seen that no animals are to be found in the 

 habitat of the parasite which would in ordi- 

 nary usage carry the seeds to these locations. 

 Seed of Razoumof- The only part, therefore, that animals play in 

 skya adhering to the dissemination of the seeds would be in 

 causing the discharge of the berries, a matter 

 of no direct value, since they are capable of quite as efficient 

 action independently. The berry of Razoumofskya is, there- 

 fore, to be classed as a sling fruit, and is probably the only 

 one of this class from the United States which has been de- 

 scribed, though many doubtless exist. 



A second point of interest in this plant consists of a fact bear- 

 ing upon its local distribution. During the course of some re- 

 cent field work in northern Arizona the writer found that 

 Razoumofskya was most successful in its attacks on the pine 

 trees along the rims of canons or along the brows of hills or 

 margins of mesas. A study of the meteorological conditions 

 shows that this method of distribution has a direct connection 

 with the vertical movements of the air. 



As the air resting on lowlands in canons or valleys is warmed 



