2l6 CHAPTER II 



This traffic is still going on on a large scale and the gradually more rigorous 

 quarantine will never be able to eliminate completely the undesirable landing of 

 unexpected and unwelcome passengers. 



As far as animals feeding upon the common agri- and horticultural plants of 

 the temperate zone are concerned, there is a marked preponderance of species 

 carried west across the North Atlantic (cf. p. 212) which is easily explained 

 by the greater number of cultivated plants transferred from the Old to the New 

 World. 



In importations connected with hothouse gardening we meet with the reverse 

 situation: the eastward transport has been strongly dominating. Above all, the 

 botanical gardens and aquariums of Europe, erected for scientific purposes, have 

 no doubt been more inclined to enlarge their collections with specimens of the 

 rich flora of North America than similar institutions of the latter region to obtain 

 European plants. It should also be observed that European animals, first arrived 

 as hothouse inquilines into North America, very often were able to spread and 

 become settled under outdoor conditions, whereas the corresponding element of 

 European hothouses often arrived from subtropical, or even tropical, parts of North 

 America and thus as a rule was prevented from leaving its artificial surroundings. 

 Only species which happened to be introduced from Europe into cold regions, 

 such as Newfoundland (certain Myriapods and Terrestrial Isopods; p. 108 a.f.) 

 or the Pacific Northwest (also some species of Carabid beetles; p. 170), have 

 also remained indoors in North America. 



Another explanation 



The main bulk of European species, animals as well as plants, which managed 

 to cross the Atlantic with man and become settled in North America, even on their 

 native continent demonstrate a high degree of dependence upon human culture. 

 Most of the plants in question are pronounced weeds and the animals, almost all 

 members of the lower soil fauna, belong to a corresponding synanthropic element. 

 Many of the insect species, for instance several Weevils {Curculiom'dae), are directly 

 bound to Crucifers, Leguminosists, and other weeds. 



These plants constitute an old element in Europe, as do the corresponding ani- 

 mals. The first civilizations of the Occident founded upon agriculture, especially 

 those of Hither Asia (Assyrians, Babylonians, &c.), were pronounced river cultures, 

 immediately bordering upon deserts and steppes. Hence man got his most im- 

 portant culture-plants, the cereals, from the unwooded land but at the same time 

 many useless plants invaded the arable land from the surrounding steppe and 



