General Physics. 133 
face, attack all the azotized, oily and amylaceous substances which they 
can assimilate ; the fecula or starch is gradually disaggregated, dissol- 
ved and absorbed, presenting a novel series of changes in the history 
of this substance. A humid state of the weather is believed to hasten 
the development of the potato fungus. 
M. Poucuer points out four stages in the process of changes. In 
the first period, the tissues of the potato are hardly discolored ; small 
clear brownish granules are distinguished at the surface of the mem- 
brane constituting the cellular tissue, especially in the intercellular spa- 
ces; the fecula of the cellules is untouched. In the second, the tissues 
are brownish ; the brown granules upon the surface of the cellules have 
multiplied, and become deeper colored; the fecula is still in a healthy 
state. In the ¢hird, the granules have become of a deeper brown color, 
and the cellules gradually become broken into shreds, the starch or fec- 
ula being not yet at all altered. In the fourth, the tissues are soft and 
grayish ; the cellular membranes are reduced to brown granulations re- 
sulting from the walls of the cellules and the granules on their surface. 
The starch grains remain “ dans leur integrité.” M. Poucuer does 
not believe that this disease results from the growth of a fungus (Bo- 
trytis infestans,) which M. Morn has detected upon the leaves of the 
potato, and regards as its origin. The affection is considered analogous 
to that which destroys cellulous fruits, such as apples, pears, &Xc. ; and 
a direct microscopic comparison is stated to favor the view. ’ 
The prevailing opinion and most observations are opposed to the 
views of M. Povcner. M. Payen has compared by analyses the healthy 
and diseased potato, and found that the fecula has actually been dimin- 
ished 20 per cent. 
V. Genera Parysics. 
62. Temperature of the Mediterranean ; (extracted from a Memoir 
on the Temp. of the Medit., by M. Aime, Ann. de Chim. et de Phys., 
8d ser., xv, 1845, p. 6.)—M. Aime arrives at the following conclusions 
from numerous observations on the temperature of the Mediterranean. 
1. Near the coast the temperature during the day is higher than in 
the open sea, and at night lower. a 
2. The mean surface temperature for the year is nearly that of the 
air; in spring and summer it is less than that of the air, and in autumn 
and winter, greater. The surface temperature is never below 50° Fah. ;, 
and sometimes reaches to 79°. ea 
3. The diurnal variation ceases to be appreciable at 20 yards, and * 
the annual variation at 350 to 430 yards. a ad 
4, On a morning afieraclear and calm night, the temperature of the 
surface is colder than that of the water several yards below. — 
