132 EXPLOITATION OF PLANTS 
enzyme through whose agency the oxidation can be 
brought about. The partial crushing of the leaf brings 
these three elements into contact; the cell-juices are 
brought to the surface of the leaf tissue, which acts as 
a sort of sponge, allowing of penetration by the air. 
Further, there can be no surprise that “‘ fermentation ” 
actually commences during rolling. We see, too, the 
meaning of discrimination in rolling. In light rolling, 
less juice will be expréssed and relatively less fermenta- 
tion probable, with the resulting tea infusion light in 
colour, lacking in body, but comparatively pungent 
owing to the proportion of unfermented tannin; with 
hard rolling, more juice is expressed and oxidised, and 
the infusion is relatively less pungent, but ae 
greater colour and body. 
Then as to the withering. If fresh, turgid feat were 
jammed into the roller, the leaf would become disinte- 
grated with the production of a leaf-mash rather than a 
“ leaf-roll.”” With a velvety, flaccid leaf, however, a 
“twist” is obtained that will appeal to the purchaser, and 
an evenly distributed rupture of the leaf-cells, which 
should promote an even fermentation. These were 
once considered to be the only objects in withering, but 
Mann and others have shown that, so long as the con- 
ditions of temperature and moisture remain satisfactory, 
the oxidising enzyme greatly increases in amount during 
the withering. Not only this, but the essential oil, to 
which the tea owes its aroma, increases during withering 
by about 15 per cent.; and this increase rises still further 
during rolling, and reaches its maximum during fermen- 
tation, constituting the second of the important changes 
accomplished in that stage of manufacture. 
