GEOGRAPHICAL DISTRIBUTION 163 



119. Escapes from Ctiltivation. — Every case of discon- 

 tinuous distribution must be carefully analyzed by itself, 

 and care must be taken not to adopt unwarranted con- 

 clusions. Thus, certain cases of discontinuity are ex- 

 plained by the escape from cultivation of forms introduced 

 by human agency for economic uses, and thus have no 

 scientific significance. The presence in the Hawaiian 

 Islands of such economic plants as sugar-cane, cocoanut, 

 and others is an apparent case of discontinuity, but these 

 plants are known to have been introduced there by man, 

 and to have escaped from cultivation. Campbell thinks 

 that the candle-nut tree (Aleurites moluccana, the source 

 of a commercial oil) and the mountain apple {Eugenia 

 malaccensis) , which now constitute the chief elements in 

 the lowland forests of Hawaii, were also introduced by 

 man, and are therefore only apparent cases of disconti- 

 nuity. Among numerous illustrations of this in North 

 America may be mentioned the paper mulberry {Brousone- 

 tia papyrifera), white mulberry {Morus alba), hemp, 

 {Cannabis saliva), stinging nettle {Urtica dioica), the day 

 lily {Hemerocallis fulva), all natives of Europe and Asia, 

 and the tree, Paulownia, a Japanese species now becoming 

 established as an escape from cultivation in New York, 

 New Jersey, the District of Columbia, and Georgia. The 

 last two species were introduced into North America as 

 ornamental plants, the hemp and white mulberry, of 

 course, as economic plants, the latter in connection with 

 the raising of silk worms. 



Attention has recently been called to the wide and rapid 

 spread of the Japanese honeysuckle {Lonicera japonica) 

 introduced in the Eastern United States from Asia. 

 Twenty-five or thirty years ago this was a comparatively 



