13 
RIPENING OF THE TOBACCO LEAF. 
The ripening process, in a normal physiological sense, refers to the 
fruit and implies the normal formation of the embryo and the filling up 
of the reservoirs of the fruit with the proper material for the young 
growing plant. The ripening of the tobacco leaf on a topped and 
suckered plant, however, implies an abuormal accumulation of organic 
matters in the leaves, brought on by preventing their transportation to 
the forming seeds and shoots or suckers, which would otherwise have 
consumed a great deal of these substances. The “ripening” of the 
tobacco leaf is, in other words, not a physiological, but a pathological 
phenomenon. By the accumulation of nicotine, oxidizing enzyms, and 
acids a State is finally reached in which the normal deep green color 
of the chlorophyll grains gives way to a yellowish color. <A “ripe” leaf 
contains per 100 square centimeters an average of 0.164 gram of mat- 
ter soluble in boiling water, while a young leaf contains only 0.066, the 
former having, therefore, for an equal surface about 2.5 times as much 
soluble organic matter as the latter. As to the total weight, a ripe 
leaf weighs from 1.3 to 1.5, on the average 1.4, times as much as an 
equal surface of a young leaf of the same plant. It is especially the 
nicotine and protein compounds that increase in the ripe leaf, a fact of 
whieh anyone can soon convince himself by a comparison of the reac- 
tion caused by phosphotungstiec acid in the juices of ripe and unripe 
leaves. The amount of water in ripe leaves averages roughly 83 per 
cent and in young leaves 88 per cent, that is, when compared in nearly 
starch-free condition after being kept for two days in darkness. 
But it is not only the increase (relative and absolute) of reserve 
materials and of products of metabolism that is brought on by topping 
and suckering; it is also the enlargement of the leaf surface, which may 
amount to over 50 per cent above the normal. The suckering exerts 
these influences to a higher degree than the topping (Behrens). A 
further influence, due to differences in topping, has been observed, low 
topping producing thicker leaves than high topping. 
An important factor is the proper time for topping and suckering. 
The suckers must be removed neither too soon nor too late. In the 
former case, too much protein would be left in the full-grown leaf; in the 
_ latter, too much nicotine might be lost from it. Goff observed that in 
moderate climates the tobacco leaves increased in weight at least to 
the thirty second day after the topping had been performed. A ripe 
leaf is recognized by the planter not only by the setting in of a 
yellowish coloration and a peculiar rough feeling to the touch, but also 
by the facility with which the lower epidermis peels oft and the leaves 
break (‘‘snap”) when folded between the fingers. 
As to the so-called ‘‘ overripe” leaves, they contain, like the young 
leaves, relatively more water and less organic matter than the ripe 
leaves. By the stoppage of the functions of the chlorophyll grains, 
which gradually change in the overripe leaves, new production of 
