METEOROLOGICAL RECORDS 163 



a few degrees above those of the winter. This feature of the 

 climate combines with a December maximum of rainfall to limit 

 the period of most rapid plant growth to two months. Bar- 

 ley sown in late November could scarcely mature by the end of 

 January, even if growing on the Argentine plains and much less 

 at an elevation which carries the night temperatures below freez- 

 ing at least once a week and where the mean temperature hovers 

 about 47° F. (8.3° C). The proper conditions for barley growing 

 are not encountered above 13,000 to 13,500 feet and the farmer 

 cannot be certain that it will ripen above 12,500 feet in the lati- 

 tude of Santa Lucia. 



The curve of mean monthly temperatures expresses a fact of 

 great importance in the plant growth at high situations in the 

 Andes — the sharp break between the winter and summer seasons. 

 There are no real spring and autumn seasons. This is especially 

 well shown in the curve for non-periodic mean monthly range of 

 temperature for the month of October. During the half of the 

 year that the sun is in the southern hemisphere the sun's noon- 

 day rays strike Santa Lucia at an angle that varies between 0° and 

 16° from the vertical. The days and nights are of almost equal 

 length and though there is rapid radiation at night there is also 

 rapid insolation by day. When the sun is in the northern hemi- 

 sphere the days are shortened from one to two hours and the angle 

 of insolation decreased, whence the total amount of heat received 

 is so diminished that the mean monthly temperature lies only a 

 little above freezing point. In winter the quiet pools beside the 

 springs freeze over long before dark as the hill shadows grow 

 down into the high-level valleys, and by morning ice also covers 

 the brooks and marshes. Yet the sun and wind-cured ichu grass 

 lives here, pale green in summer, straw-yellow in winter. The 

 tola bush also grows rather abundantly. But we are almost 

 at the upper limit of the finer grasses and a few hundred feet 

 higher carries one into the realm of the snowline vegetation, 

 mosses and lichens and a few sturdy flowering plants. 



For convenience in future comparative studies the absolute 

 extremes are arranged in the following table : 



