212 TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 
particular insect, but they do not deny commerce with other 
nations. No one who has seen the map and account of the range 
of Bombus and Aconitum in Drude’s Pflanzen Geographic’ can 
doubt that the range is, in some cases, influenced by the best 
possible insect visitor. 
If we turn next to those plants which may be called the camp- 
followers of man or his domesticated animals or plants, we know 
that, whenever virgin soil is broken, a deadly struggle occurs 
between the domestic plant with its weedy clients and the natural 
vegetation. The seeds of Egyptian weeds have been found in the 
prehistoric lake villages of Italy. I have gathered, ¢.g., in Tripoli, 
to quote my herbarium book, No. 3196, Urtica membranacea, 
Poir, “ Aaron Arbib’s orange gardens, rather sandy ground ; 
sheltered. January 9th.” This is an American weed brought 
with the oranges. A very interesting discussion of this point is 
to be found in the New Jersey Agricultural Experiment Station 
report.* Mr. Halsted shows there clearly how weeds of different 
origins have traversed the country: Papaver dubiwm, Linn., from 
Europe, travelling 25 miles in 15 years (lc, p. 321), The 
Argemone mexicana, Linn., has invaded the country from tropical 
America. Abutilon Avicenne, Gaertn., has come from India and 
is working westward, whilst Xanthiwm canadense, Mill, and 
others are native plants which have become weeds of cultivation, 
just as our common plants did long ago. 
I feel pretty certain that at least 100 dicotyledons of the 
“ London Catalogue,” and fully half the grasses, are either arti- 
ficially introduced by man, or have been brought accidentally. 
This is about 12 per cent. of the flora, and probably a very long 
way under-estimated. For all these the limit is human agriculture, 
and, to a large extent, the skill in farming of a particular district. 
Again, plants of fresh water are very widely distributed. This 
is probably through the fact of water birds carrying the seeds ; 
the extremely wide range of ducks, ¢.g., is notorious. It is 
coneeivable that a fresh-water plant might pass right round the 
earth in four seasons if we take this into consideration. The 
1Drude, Pflanzen Geographie, pp. 122 and 123. This is taken from 
Kronfeld, Botan. Jahrbuch. fiir Systematik, Bd. XI., p. 19. 
2 Annual Report, Botanical Department (New Jersey Agricultural 
Experiment Station), 1891. 
nk Ci ON 
