189 
favorable to vegetation, and the same may be said of high plateaus 
pee radiation is more powerful. 
. The isanthesic lines, or lines of simultaneous flowering, do not 
oa any parallelism at different periods of the year; thus, the 
line which shows where the lilac blooms on a giv en day of the month 
passes ten days afterwards through another series of places where 
the same phenomena is then occurring. 
Now, the zone comprised between these two lines has not the same 
breadth throughout its whole extent, as would be the case with a zone 
between two parallels of latitude. It is not even constant, since, for 
example, a month later the isanthesic lines will have quite different 
forms, and localities that were backward as compared with others 
may then be in advance. 
8. The falling of the leaves is a phenomenon which in our climate 
depends as much upon the current temperature as upon those which 
have preceded. It 1s generally controlled by the first cold of autumn. 
FRITSCH. 
Karl Fritsch (1881) gives the results of about ten years’ observa- 
tions of plants growing in the Botanical Garden at Vienna (1852— 
1861). His list of plants embraced all those recorded in the previous 
lists of Quetelet, Sendtner (1851), and his own, in all 1,600 species 
and varieties, but of which he has only used 889. The epochs ob- 
served by him, as uniformly as possible throughout the ten years, 
were the following: 
(1) ‘The first visibility of the upper surface of the leaf. 
(2) The complete development of the first flower. 
(3) The complete ripening of the first fruit. 
(4) The date at which a tree or bush has lost all of its foliage. 
Having endeavored in vain to establish a connection between the 
moisture of the air and the growth of the plant, and finding it imprac- 
ticable to take account of the moisture in the earth, Fritsch resolved 
to reject observations made during special droughts or floods or other 
abnormal conditions and to consider only the sum of the average 
daily temperatures. These mean daily temperatures he deduced from 
the observations at 6 a. m. and 2 and 10 p. m., made at the Central 
Meteorological Institution in Vienna, where the thermometer was 
about 50 feet above the ground. The summation of the mean daily 
temperatures for comparison with phenological phenomena counts 
from the 1st of January to the date of the observed epoch, and omits 
all days whose mean temperatures are 0° Réaumur or lower than that. 
A comparison of the observations made on successive years on the same 
plant shows that the time of blossoming is uncertain by only one or 
two days in 96 per cent of all the plants, and the so-called “ tenipera- 
ture ” or “ thermal constant ” is uncertain by 3 per cent of its amount 
or less, in 97 per cent of all the plants. Similarly, for dates of ripen- 
