87 



When cultivating monocarpic plants, such as vegetables, the injury due 

 to an otherwise suitable exposure, viz., injury from spring frosts, is felt 

 only when the small plants are put out early in spring. There is still greater 

 injury to sensitive polycarpic plants to which our nut trees belong. Here, 

 with a favorable, warm exposure, there is a failure of the harvest, while in 

 the same year nuts are produced abundantly with raw exposures. In the 

 hrst case the young shoots and blossom buds, forced out earlier by the great- 

 er warmth, are blasted by the night frosts which have not harmed the less 

 developed specimens found in high raw exposures. 



In garden plantations, when taking advantage of such positions, ont 

 attempts to avoid the disadvantages of the spring frosts by holding tht 

 plants back artificially. This is done by leaving them covered longer, either 

 by heaping snow on them or by increasing the mats and litter. With fruit 

 trees snow, ice and mulching are heaped about the base in order to keep the 

 soil cool as long as possible and thus retard the root activity. 



The cold northern exposure is best for meadows and forests. Eastern 

 slopes are unsuitable if the soil is sandy because they dry out more quickly. 

 They are therefore more valuable if the soil is heavy. The reverse is true 

 of the damp westerly side. Holzner\ comparing a slope at 50° north 

 latitude, inclined about 10° southerly, v^-ith another with a 10° northerly in- 

 clination, also took into account the difference in warmth which can be 

 called forth by an inclination of lo'^, when all other condtions are assumed 

 to be equal. The sum total of the sun's rays falhng upon this soil bears the 

 proportion on the south and the north slopes of approximately three to two. 



Wollny's- experiments on the warming of field lands deserve 

 especial mention. In this work Kerner's"' observations are cited, show- 

 ing how differently the several sides of a hill warm up. These obser- 

 vations follow closely upon the preceding ones. The mean found by 

 three years of observation showed that the exposures may be arranged as 

 follows, decreasing according to their warmth. The warmest exposure was 

 S. W. then followed S., S.E., W., E., N.E., N.W. and N. This scale shows 

 that in reality the different exposures do not act as one would first suppose 

 theoretically. It would seem first of all that with the sun equally high above 

 the meridian the heating would be equally strong and that, therefore, the 

 southeast side would receive the same amount of warmth as the southwest 

 side. Kerner explains that this is not actually the case by stating that in the 

 afternoon the sun at the same height acts more powerfully because the satu- 

 ration of the air with water moisture is lower then than in the morning hours 

 on which account the absorption of the sun's rays is less in the afternoon. 

 Lornez* gives still another reason. On the southwest side, the dew 



1 Holzner, Die Beobachtungen iiber die Schiitte der Kiefer oder Fohre und die 

 Winterfarbung- immergriiner Gewachse. Freising 1877. 



- Wollny, Untersuchungen iiber den Einflufs der Exposition auf die Erwarmung 

 des Bodens. Forschungen auf rtem Gebiete der AgriPculturphysik. Vol. I, p. 263. 



3 Kerner, Ueber Wanderungen des Maximums der Bodentemperatur. Zeitschr. 

 d. osterr. Ges. f. Meteorologie. Vol. \'I, No. 5, pp. 65 ff. 



4 Lorenz und Rothe, Lehrbuch der Klimatologie. Wien 1874, p. 306. 



