244 
northward we have a greater amount of possible sunshine during the 
growing period, although the actual sunshine is very materially 
diminished by the quantity of cloud and fog. Tisserand calls atten- 
tion to the maximum possible duration of sunshine as given in the 
following table for the season of spring wheat from sowing to 
ripening: 
| Maxi- 
atitude |e Correspond- 
north. Soe ing locality. 
tion. 
QF Hours. 
48 30 | 1,996 | Alsace. 
59 «(O 1,795 Christiania. 
59 30 2,187 Halsno. 
40 2, 376 Bodo. 
68 00 2,472 Strand. 
69 30 2,486 Skibotten. 
These numbers of possible hours of sunshine should be diminished 
to actual hours of sunshine on account of cloudiness. Moreover, 
actual actinometric observations would have shown that owing to the 
atmospheric absorption the efficiency of the sunshine is less at low 
altitudes and, therefore, at high latitudes. But in the absence of 
fundumental climatic data Tisserand 1s probably correct in conclud- 
ing that the temperature of the air has apparently little to do, in and 
of itself, with the duration of the time from sowing to ripening, but 
that this depends principally on the sunshine, so that at northern 
latitudes the wheat ripens best in localities that have the least cloudi- 
ness or the sunniest exposure. On the other hand, the temperature 
of the air does appear to materially affect the chemical constitution 
of the grain, since the northern crops are richer in hydrocarbons, 
and the proportion and quality of the starchy principle increases 
and the nitrogenous compounds diminish as the locality approaches 
the equator. 
The acclimatization of plants is accompanied by notable changes 
in their nature; frequently the leaves increase in size relatively to 
the rest of the plant, and their colors are more pronounced, as if the 
plant sought to supplement the low temperature by a more complete 
absorption of the solar rays. A similar change as to the leaves and 
colors takes place in the flora of high mountains as compared with 
that of the plains below. The aromatic principles of plants are also 
developed in a remarkable manner in high latitudes. Thus the beans 
have a more decided flavor in Norway in proportion as we go north- 
ward, and at Alten (lat. 70° N.) the most aromatic cumin (Cuminum 
cyminum) of all Europe is cultivated. 
The incident sunshine seems to be the productive climatic element 
in effecting the growth of plants; it furnishes the total vis viva, or 
