386 
5. 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, 
undesirable species. Mr. L. H. Dewey says: 
“Tt 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 acci- 
dentally introduced by means of seeds, 
bulbs and root stocks attached to nursery 
stock or among the pellets of earth about 
the roots of nursery stock. The extraordi- 
nary development, of late years, of commerce 
in nursery stock has undoubtedly been re- 
sponsible for the intracontinental carriage 
of many species of plants in this way. 
Instances of the accidental spread of 
larger animals by man’s agency are neces- 
sarily 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 practi- 
cally 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 acci- 
dentally across the ocean in any one of the 
SCIENCE. 
[N.S. Von. VI. No. 141. 
many ways in which the accidental trans- 
portation of plants and insects may be 
brought about, and by virtue of their re- 
markable 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 restrictive, whence 
it follows that comparatively 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 here, mainly 
in the vicinity of the seaport towns of 
the Atlantic coast. 
With the earthworms a striking situa- 
tion exists. It has been shown that, ‘ with- 
out a single exception, the Lumbricidz 
from extra-European regions are identical 
with those of Europe; there is not a vari- 
ety known which is characteristic of a for- 
eign 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. In the words of Wallace : 
“The families and genera of insects are 
so immensely numerous, probably exceed- 
ing fiftyfold those of all other land ani- 
mals, that for this cause alone it would be 
impossible to enter fully into their distribu- 
tion. It is also quite unnecessary, because 
many of the groups are so liable to be 
transported by accidental causes that they 
afford no useful information for our subject, 
while others are so obscure and uninterest- 
ing that they have been very partially col- 
lected and studied, and are for this reason 
equally ineligible.” 
Nevertheless,the time has already arrived 
with some groups, and is not far distant 
*F. E. Beddard, Text Book of Zoogeography, 
Cambridge, 1895, p. 153. 
