68 
AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
these varieties may be affected with internal decline. Data thus far ob¬ 
tained do not indicate any marked difference in varietal susceptibility. In 
some localities the Eureka is reported to be more susceptible while in other 
localities the Lisbon is said to suffer most, but so far the data do not confirm 
these reports. 
Seasonal Appearance. The trouble usually appears with the beginning 
of warm weather in June and continues during the summer and fall until 
November or December. However, some lemons that are slow in attaining 
a desirable picking size may be allowed to remain on the trees for a longer 
period than usual, and consequently a few lemons showing internal decline 
may appear in the packing houses at almost any time during the winter or 
even in the early spring months. 
Age of Trees. Internal decline has been found on trees of all ages 
ranging from 3 or 4 years up to 50 years. It is often the case that the fruit 
on young, thrifty trees with heavy foliage is worse affected than that on 
older trees with less dense foliage. 
Age of Fruit. The terms “tree-ripe,” “silver,” “light-green,” and 
“dark-green ” are used in the lemon industry to designate lemons in different 
stages of maturity as indicated by their color. Tree-ripe lemons are those 
which remain on the tree until they have attained their mature yellow color; 
silver lemons are those which are picked at a time when most of the chloro¬ 
phyll has disappeared from the fruit, leaving it a very light greenish yellow; 
light-green and dark-green lemons are picked according to standardized 
sizes. They are younger than the preceding kinds but are sufficiently 
mature for picking. When lemons are picked while they are yet green, 
they are either allowed to color naturally while in storage or are artificially 
bleached before being placed on the market. The lemons that are picked 
while green possess the most desirable commercial qualities because they 
have a higher acid content and are less susceptible to the attacks of diseases. 
In some cases internal decline is found only in the tree-ripe fruit, but it 
often appears also in the silver, light-green, and dark-green fruit from the 
same grove. The tree-ripe fruit usually shows the greatest percentage of 
the trouble, sometimes as much as 95 percent being affected. However, 
in “bad years” as much as 60 percent or more of the green fruit in a given 
pick may be affected. 
Symptoms 
Green Fruit 
External Symptoms. It is often impossible to determine without cutting 
the fruit whether or not it is affected. In some cases the trouble may be 
detected by a partia loss of luster at the stylar end. Another indication 
is the development of a yellow or orange-yellow color on a quarter or more 
of the stylar end while the remainder of the lemon is still green; even this 
appearance, however, is not a sure indication of internal decline. 
