104 ERYTHEA. 
idle to speculate on such a fascinating subject, it nevertheless 
appears to me that any further injurious additions we are 
likely to encounter here will most probably be natives of 
South America or the Eastern States. The majority of the 
noxious European weeds are already naturalized here, and 
illustrate in their own peculiar way how impossible it is for 
any one to anticipate their behaviour under changed condi- 
tions of soil and climate. Brassica nigra can scarcely be 
considered as noxious in Europe but B. Sinapistrum is in 
many districts the bane of the farmer’s life. In the states of 
Pennsylvania and New York it is somewhat troublesome in 
the grain fields. Mallow, hoarhound, knapweed, the bur 
clover and others, surprise us by their fertility and ready 
adaptation to western soils, The reason of this change in 
ratio of the different species is obviously the drought. Many 
of the annuals in Europe are abundant because there the 
moister soil and climate favor their perpetual growth. Here 
the shorter spring and the dry summer hasten the ripening 
and dissolution of the weaker annuals so that those like 
Spergula arvensis can neyer become here the pests they 
are in many parts of the Old World. On the other hand, 
the deeper rooting kinds such as the mallows, are not so 
adversely influenced by drought; indeed, in some instances 
they are rather favorably affected by it. 
The rapid transformation which this section of the country 
is undergoing in its conversion from waste and brush land to 
orchards and farms, will lead to many changes in the quality 
and conditions of the soil, and undoubtedly will affect ina 
great measure the quality and distribution of our naturalized 
species; and such a record as is here made may in the future 
afford a basis for some interesting comparisons. 
