440 
AMERICAN JOURNAL OF BOTANY 
[Vol, 8, 
parison is not so instructive as one made from cleared and uncleared leaf 
portions taken from paired plants and studied by the same methods. 
However, these data compare favorably with the results obtained from the 
study of the cleared and uncleared leaves of the undetermined species of 
Vitis shown in table i. It will be noted that in both cases the uncleared 
leaves show vein-islet areas from two to three times larger than those from 
cleared and stained leaf portions. 
Discussion 
The above data show that an}^ study of leaf venation made from un- 
cleared leaves is wholly unreliable. The varying thickness and chlorophyll 
content of leaves render many of the smaller veins entirely invisible. Fur- 
thermore, some unpublished results obtained by Heinicke' do not corrob- 
orate the preliminary venation studies of uncleared apple leaves made by 
Benedict. Heinicke finds no correlation between vein-islet area and the 
age of a large number of apple varieties. These are of known age, i.e., it 
is known when they originated as seedlings. 
The results herein presented do not show a single instance in which the 
leaf venation might be taken as an index of-the relative ages of the plants 
in question. While working with yearling Citrus seedlings, a number of 
grape-fruit leaves were obtained from some of the oldest trees in the vicinity 
of Miami, Florida, and it was found that the venation of the leaves from 
the yearling plants was identical with that from the older trees. A similar 
condition was found in regard to the venation of some orange leaves taken 
from a plant growing in the Sage greenhouse at Cornell. This plant was 
probably ten or fifteen years of age. These similarities in venation seem 
to be indicative of something more than mere coincidences. 
As intimated at the beginning, it is highly desirable that more data be 
secured bearing upon this problem. There are certain phases which require 
more elucidation before satisfactory conclusions can be derived. It may 
be that the venation of the uncleared leaves of Vitis vulpina and other 
plants with which Benedict worked shows some correlation with age which 
the cleared leaves fail to reveal. Such a possibility, however, does not 
seem tenable. 
Just as this goes to press the following statement comes from August 
Henry, Royal Society of Dublin: 
I tried this [venation vs. age] in the various species and hybrids while working on my 
paper on "The Origin of the London Kane." In this I dealt with the genus Platanus (Proc. 
Royal Irish Acad.) without any very conclusive results. Here the question lay in regard 
to whether trees produced of cuttings were as old as the original, or only as young as the 
time the cuttings were started. 
Summary and Conclusions 
I. From seventeen to sixty- two percent of the vein-islets are invisible 
in uncleared leaves of Vitis sp. 
^ A. J. Heinicke, assistant professor of horticulture, Cornell University. 
