288 BOTANICAL GAZETTE | OCTOBER 
as great as with us. The strongest pressure observed was somewhat more 
than eight atmospheres in Schzzolobitum excelsum Vog. 
“3, The sap pressure varies, often very markedly, in one and the same 
plant within twenty-four hours. This phenomenon cannot be ascribed to 
daily periodicity alone, but must be referred to the influence of external 
factors, especially to the transpiration, which even in the tropics, is very 
copious."’— C. R. B. 
PROFESSOR WIESNER presented at the June meeting of the Imperial 
Academy of Sciences in Vienna a memoir entitled “Contributions to the 
knowledge of the photo-chemical climate in Arctic regions.’’ His results 
(translated from Osterreichische Botanische Zeitschrift 48:360. 1898) are as 
follows : 
“1, In high northern regions (Advent bay, Tromsé) the chemical intensity 
of the total daylight, with equal elevation of the sun and equal cloudiness, . 
is greater than in Vienna and Cairo, but less than in Buitenzorg, Java. At 
rondhjem the same is true, but with a considerably greater approximation 
to the conditions at Vienna. 
“2, With a completely overcast sky, the intensity of the light was observed 
to increase much more regularly with the height of the sun at Advent bay 
than in any other vegetation region observed. 
“3. At Advent bay with equal elevation of the sun and equal cloudiness, 
the chemical intensity of light in the morning and afternoon were nearly 
equal; however, in most cases the afternoon intensity is somewhat greater 
than the morning. 
“4, The greatest intensity of the total daylight and the diffuse light is to 
be observed in all regions upon a vertical surface, which faces the sun; the 
smallest upon the opposite vertical surface. The intensity upon the inter- 
mediate planes lies somewhere between that of the first two. 
“5. Even with a completely clear sky, the distribution of the light inten- 
sity upon the illuminated vertical plane is not completely symmetrical. 
6, With increasing elevation of the sun, the direct light (Vorderlicht, bt5 
the average light falling upon the vertical plane) in comparison with the sky 
light (Oder/icht, 7. e., the total daylight measured upon a horizontal plane) 
diminishes. In Advent bay at the beginning of August, the ratio of the 
direct light to the skylight is as 1:1.5-2.2, whereas in Vienna in May this 
ratio may exceed 1:4. 
“7. For days of equal elevation of the sun at midday the daylight 
totals in Arctic regions are considerably greater than in temperate latitudes. 
At the beginning of August the average daylight total at Advent bay is about 
two and one-half times greater than on similar days in Vienna (at the begin- 
ning of November and February). 
“8. The light climate of the high northern vegetation region is charac- 
