DISTRIBUTION 01^ I.. D^CI^MUNEATA. 23 



in several instances that as new routes of travel become more and more 

 commonly used, as, for example, those leading to irrigated arid lands, 5. ros- 

 tratum and L. intermedia soon increase along these lines and enter areas not 

 hitherto occupied by them. 



LEPTINOTARSA DECEMLINEATA PREVIOUS TO t859. 



Greater doubt exists concerning the original distribution of this species 

 than of that of any other. I have shown it to be highly probable that the 

 movements of Spanish travel and commerce resulted in the dispersal of 

 Solanuvi rostratiun, an essentially tropical plant, into Texas, New Mexico, and 

 parts of Arizona. We know that this plant was and is now found farther north 

 than the most northern limits of Spanish activity, and we may now inquire 

 into the factors which were possibly active in its dissemination over the Great 

 Plains as far as the boundary between the United States and Canada. 



Solanum rostratum grows best about places where cattle congregate, 

 especially about drinking places and wallows, although it is found else- 

 where. Its seed pods are well adapted to being transported by large mam- 

 mals, being armed with hooks and spines, which provide efficient means 

 whereby they are held in the hair of the cattle and thus carried often for 

 long distances. That this method of transportation has been the means of 

 spreading this plant over the country to the east of its original habitat is a 

 fact known from many records. I have often observed burro trains, cattle, 

 and horses which had gathered at places where Solanum rostratum was grow- 

 ing to leave these places with its burs entangled in the hair of their coats 

 so firmly that a considerable journey might be completed without their 

 becoming dislodged. This plant is therefore liable to be carried in any 

 direction by cattle, but principally in the lines of travel followed by pack- 

 trains. The heavy seeds, devoid of any means of dispersal, are largely 

 dependent upon this means for their dissemination. If we grant that Spanish 

 caravans brought this plant into Arizona, New Mexico, and Texas, and that 

 without outside assistance it would be impossible for it to spread long dis- 

 tances to the north of the range of Spanish activity, what agencies were 

 present in this portion of North America at this time that would be able to 

 bring about this result ? 



The agents most likely to do this seem to be, first, migratory mammals ; 

 second, wandering bands of men, and third, possibly, birds. Other agencies, 

 such as wind, water, and storms, are clearly of little effect in this case. The 

 third agency suggested is also of such slight importance, if of any, that we 

 may as well discard it at once. Of the two remaining possibilities it seems 

 to me that the first has in this case by far the stronger hold upon our atten- 

 tion and the greater chance of being a true cause of dispersal. It is known 

 that huge herds of bison on the Great Plains^ migrated south into Texas 



^Although the bison ranged much farther east at this time, the huge herds of the Great 

 Plaint seem to have been distinct from the eastern bison. 



