Mar., 1923] 
BARTHOLOMEW — INTERNAL DECLINE 
123 
in all, the tissue had broken down, thus leaving small circular openings about 
1 mm. in diameter adjacent to each main vascular bundle. These openings 
have been termed '‘drying-out holes.” Cutting of control lemons at the 
time these branches were taken from the tree showed that these lemons 
were in a normal condition at the beginning of the experiment. Thousands 
of lemons taken from dry portions of groves and cut have shown these 
drying-out holes, while comparatively few or none of the lemons from the 
more moist portions of the same groves showed them. The variation in 
moisture content in different parts of a grove may be due to such factors 
as differences in soil texture or an uneven distribution of irrigation water. 
That there must be some relation between these drying-out holes and 
the appearance of internal decline is indicated by the fact that practically 
every lemon having decline shows these holes when it is cut for examination. 
This experiment coupled with the field observations indicates that this 
collapse of tissue, caused by the withdrawal of water from the fruit, is the 
first visible step in the production of internal decline. 
The results of the preceding 5 experiments show very clearly that the 
lemon fruits act as water reservoirs for the leaves. When the roots fail 
to supply adequately the demand of the leaves for water, the leaves begin 
to draw it from the fruits. In a climate such as exists in the inland lemon¬ 
growing districts of California, the leaves will begin to draw water from 
the fruits even before the soil moisture has become very materially depleted. 
On going into a grove in the afternoon on a warm summer day when the 
temperature is near ioo° F. and the psychrometer shows a humidity of 
20 percent or less, the lemon fruits are found soft to the touch even though 
the soil moisture content may be well above the wilting coefficient of the 
leaves. Upon examination of the same lemons the following morning 
they will be found turgid. This condition becomes especially noticeable 
when there is a wind blowing, since this increases the rate of evaporation 
from the leaves. The withdrawal of water from the fruits by the leaves 
is an important factor in irrigated districts such as this, because, if the 
water supply in the soil becomes too low, or if climatic conditions remain 
unfavorable too long, not only the fruits but also the leaves may be caused 
to fall from the trees. 
In connection with the foregoing statements it might be well to empha¬ 
size the fact that, at least in the case of such plants as citrus trees, which 
may retain their fruits from several months to a year or more, the term 
“wilting coefficient” of the soil, as usually applied, has little significance. 
There can be no doubt that water may be withdrawn from the fruit to an 
injurious extent by the leaves long before there is any sign of wilting in the 
leaves. For such plants as the citrus fruits it would be interesting and 
profitable to have determined a wilting coefficient based on fruit rather 
than on leaf conditions. However, this would probably be difficult except 
as a coefficient might be worked out for each individual kind of fruit. 
