October 21, 1897] 



NATURE 



60: 



understanding of the life-hislory and habits of the species. Even 

 then there may be danger, as with a new environment habits 

 frequently change in a marked degree. 



Accidental Introouctions. 



The agency of man, however, has been more potent in ex- 

 tending ^the range of species and in changing the character of 

 the faunas and floras of the regions which he inhabits by means 

 of accidental importations. 



The era of accidental importations began with the beginning 

 of commerce, and has grown with the growth of commerce. 

 The vast extensions of international trade oi recent years, every 

 improvement in rapidity of travel and in safety of carriage of 

 goods of all kinds, have increased the opportunities of accidental 

 introductions, until at the present time there is hardly a civilised 

 country whicii has not, firmly established and flourishing within 

 its territory, hundreds of species of animals and plants of foreign 

 origin, the time and means of introduction of many of which 

 cannot be exactly traced, while of others even the original home 

 cannot be ascertained, so widespread has their distribution 

 become. 



These accidental importations would at first glance seem to 

 have been more abundant with plants than with animals, since 

 the opportunities for the carriage of seed, especially flying or 

 burr-like seed, and especially when we consider the vitality of 

 this form of the plant organism, are plainly manifold, but 

 possibly even this obvious generalisation must be modified in 

 view of the multitudinous chances for free travel, which the 

 smaller insects have under our modern systems of transporta- 

 tion. 



The agencies which have mainly been instrumental in the 

 accidental distribution of plants are : 



(1) Wind storms. It is obvious that light-flying seeds may be 

 carried many hundreds of miles by hurricanes, and may fall in 

 new regions. 



(2) Water. This is a very important agency in the distribution 

 ■ A plants upon the same continent, but less important as affect- 

 ing intra-continental distribution. Still, they may be carried by 

 this means from one island to another adjoining island, and when 

 lodged in the crevices of the driftwood they undoubtedly travel 

 greater distances. 



(3) Birds. Seeds are frequently carried great distances by 

 birds. Many of the larger seeds will germinate after passing 

 through the alimentary canal of a bird, and may thus be eaten 

 at one point and voided with the excrement at a widely distant 

 point. It has been shown, for example, that the local distribution 

 of Rhus toxicodendron is greatly affected by the carriage and 

 distribution of the seed in this way by the common crow. 

 Smaller seeds are carried in earth on the feet of birds. Dar- 

 win's example of a wounded red-legged partridge which had 

 adhering to its leg a ball of earth weighing 6.^ ounces, from 

 which he raised thirty-two plants of about five distinct species, is 

 an evidence of the possibilities of this agency, while his experiment 

 with 6f ounces of mud from the edge of a pond which produced 

 537 distinct plants, an average of a seed for every six grains of 

 mud, is still more conclusive. 



(4) Ballast. This is the first of the distribution methods which 

 rnay be combined under the head of "agency of man." The 

 discharge of earth ballast by vessels coming from aliroad has 

 been a notable means of distribution of plants by .>,eed. We 

 have just seen how many seeds may germinate from a very small 

 lump of earth, and the possibilities in this direction of the many 

 thousands of pounds of discharged ballast are very great. In 

 fact, the ballast grounds in the neighbourhood of great cities are 

 invariably favourite botanical coUecling spots ; they have usually 

 a distinctive flora of their own, and from these centres many 

 introduced plants spread into the surrounding country. 



(51 Impure seed. The great industry in the sale of seed 

 which has grown up of late years is responsible for the spread 

 of many plant species, principally, it must be said, unde.sirable 

 specie-s. Mr. L. H. Dewey says : " It may be .safely asserted 

 that more of our foreign weeds have come to us through impure 

 field and garden seeds than by all other means combined." 



(6) The packing material of merchandise. The hay or straw 

 used in packing crockery, glassware, or other fragile merchandise, 

 is a frequent carrier of foreign seeds. Such goods frequently 

 reach the retailer without repacking, and the hay or straw is 

 thrown out upon the fields, or used as bedding for domestic 

 animals and carried out with the manure 



(7) Nursery stock. Plants are often accidentally introduced by 



NO. 1460, VOL. 56] 



means of .seeds, bulbs and root stocks attached to nursery stock, 

 or among the pellets of earth about the roots of nursery stock. 

 The extraordinary development, of late years, of commerce in 

 nursery stock has undoubtedly been responsible for the intra- 

 continental carriage of many species of plants in this way. 



Instances of the accidental spread of larger animals by man's 

 agency are necessarily wanting. Of the smaller mammals the 

 house rat and the house mouse have been accidentally carried in 

 vessels to all parts of the world, and have escaped and established 

 themselves, the former practically everywhere except in boreal 

 regions, or only in its southern borders, and the latter even as far 

 north as the Pribyloff Islands, as I am informed by Dr. Merriam. 

 Small reptiles and batrachians are often accidentally carried by 

 commerce from one country to another ; but although there are 

 probably instances of establishment of such species, none are 

 known to me at the time of writing. 



Land shells are often transported accidentally across the 

 ocean in any one of the many ways in which the accidental 

 transportation of plants and insects may be brought about, and by 

 virtue of their remarkable power of lying dormant for many 

 months are able to survive the longest journeys. The conditions 

 which govern the establishment of species in this group, how- 

 ever, seem somewhat restricted, whence it follows that com- 

 paratively few forms have become widespread through man's 

 agency, although Binney mentions a number of European species 

 which have been brought by commerce into the United States and 

 have established themselves there, mainly in the vicinity of the 

 seaport towns of the Atlantic coast. 



With the earthworms a striking situation exists. It has beery 

 i .shown that, " without a single exception, the Lumbricidre from , 

 extra- European regions are identical with those of Europe ; 

 there is not a variety known which is characteristic of a foreign 

 country." Careful consideration of the evidence seems to show 

 that this is due to accidental transportation by the agency 

 of man. 



Comparatively little has been done in the .study of the 

 geographical distribution of insects. 



The insects which are accidentally imported, are carried in 

 three main ways. Either (i) they are unnoticed or ignored 

 passengers on or in their natural food, which is itself a subject 

 of importation, such as nursery stock, plants, fresh or dried fruit, 

 dried food-stuff's, cloths, lumber, or domestic animals ; or (2) 

 their food being the packing substances used to surround mer- 

 chandise or the wood from which cases are made, they are thus 

 brought over ; or (3) they may be still more accidental passen- 

 gers, having entered a vessel being loaded during the summer 

 season, and hidden themselves away in some crevice. The 

 coleopteri-sts (Hamilton and Fauvel)make a distinction by name 

 among these classes, calling the first group "insects of com- 

 merce," and the latter "accidental importations." 



The practical point to which we must come, after summarising 

 all that has been shown, is that since so many species have been 

 imported by pure accident, and have succeeded perfectly in 

 becoming acclimatised, may not much be accomplished by 

 wisely-planned and carefully-guarded introductions? The work 

 of Mr. Albert Koebele, first for the United States Government, 

 afterwards for the State of California, and now for the Hawaiian 

 Government, is certainly an indication, taken in connection with 

 what we have shown, that thorough experimental work with 

 predaceous and parasitic insects promises, in especial case', 

 results of possibly very great value. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 

 Oxford.— The announcements o. professors, readers Uni- 

 versity teachers, and lecturers for Mich.ielmas term include the 

 following :— A course of lectures on elementary pathology by 

 the Regius Professor of Medicine, Dr. f. Burdon-Sanderson. 

 A practical course of instruction in general pathology by the 

 University lecturer, Dr. Ritchie. The Lichfield Lecturer in 

 Clinical Surgery, Mr. W. L. Morgan, will lecture on elementary 

 surgery. The Professor of Human Anatomy, Prof. A. Thom- 

 son, will lecture on human osteology. The Lecturer in Materia 

 Medica, Mr. J. E. Marsh, will give at the University Museum 

 a practical course of organic chemistry. The Savilian I'rofessor 

 of Geometry, Prof. W. Esson, will lecture at Merton College 

 on (i) the theory of plane curves ; (2) synthetic geometry. The 

 Savihan Professor of Astronomy, Prof. H. H. Turner, will 



