360 J. W. Langley—Chemical Affinity. 
a harvest of thirty to forty times the quantity that was sown 
alternates in this climate with years of no harvest at all.” 
As is well known, the native plants withstand the lowest tem- 
peratures of the Siberian winter. 
eturning to Hurope we have seen that even the climate of 
tae northern parts of the British Isles is not suited for many 
vegetables and other cultivated plants. 
t is Germany which has a climate adapted to almost all 
the plants of the temperate zone and to those commonly culti- 
vated. We see the vine in this country ascend farthest to the 
north, while corn and all vegetables ripen their seeds perfectly. 
The climate is clearly that best suited for the vegetation of 
this latitude. ; 
Now, if we compare the mean temperature of July in Ger- 
many with the mean for the latitude (for 50° N.—62°) cal- 
culated by Dove, we find that even in this country the summer 
temperature is, in general, only a few degrees above the calculated. 
Germany is crossed in July by the isotherm of 68°, and Britain 
by that of 59°; but the difference in vegetation is not cause 
by a difference in mean temperature of nine degrees, but by 
the difference in the days of sunshine. ° 
us we come to the conclusion that a mixed climate with 
relatively mild winters (the anomaly of temperature for January 
is for Germany about +9° on the 50th degree of latitude) and 
warm sunny summers is the condition best suited for the vege- 
tation of the temperate zone. 
Flushing, June, 1884. 
Art. XLIV.—-Chemical Affinity; by Joun W. LANGLEY, 
An rbor, Michigan. 
[Address before Section ‘‘C” of the American Association for the Advancement 
of Science, Philadelphia, 1884. ] 
In reviewing the history of each living being and of every 
intellectual conception we are at once made aware of a law of 
growth, the most general and fundamental possible, namely, 
that of development, or progression along what often seems 
be a predetermined line whose constraining influence 18 %° 
powerful that it is only by following it that the organism can 
escape destruction. oo 
Development, while it may be continuous, both for the indi- 
vidual and for the race when broadly looked at over large 
intervals of time, is, on the other hand, a process which in 118 
details is constantly interrupted both by alierations of direc: 
tions and by arrests of action which may even go so far as to 
cause retrograde metamorphoses. 
% Middendorff, p. 720. 
