v7. ‘ORIGIN OF MOULD. 497 
wards the top. The defcription will, perhaps, be 
better underftood by fig. 3. 
Mould is at firft of a moft’beautiful white ; it 
next acquires a yellowifh tint, and at -laft black- 
ens; however, the heads grow much blacker 
than the ftalks and branches. The origin and 
increafe of mould is neurly in proportion to the 
‘heat of the atmofphere ; its appearance and ve- 
getation are never more fudden than during the 
heats of fummer. A fubftance which dees not 
exhibit a fingle ftalk of mould at night, -will of- 
ten be covered in the morning by mould, which 
thas then attained its full fize and maturity (1). 
It does not increafe fo much in height as in thick- 
nefs, and the ‘heads, already black, are always of 
‘larger fize than when they were -young and 
“white. 
~Mould never rifes fo beautiful and vigorous as 
when vegetating under fome veflel or receiver, 
‘providing the communication with the external 
-and internal air remains. The.reafon is evident. 
N43 The 
(1) Bradley remarks that the {eed of mould has vege- 
‘tated in three hours, and in about fix more, the plant-had 
attained its perfect fize, Philofophical Tranfadtions, 1729, 
- yp. 491. However, fome mould takes much longer time. 
Nay, it is often very long before mould is produced on .a 
fubftance, either from abfence of the feeds, or the fub- 
ance not being well adapted for its vegetation. —T. 
