422 
noted and seemed to merit this preliminary 
note, because of the ease with which it may be 
recognized without apparatus by fruit growers 
as well as by botanists. 
The smallest veinlets of the leaf form a 
continuous network and the meshes of this 
network are areas of parenchymatous tissue. 
The size of these areas is not only remarkably 
uniform in a mature leaf but is directly de- 
pendent upon the age of the plant upon which 
the leaf is growing. The older the plant, the 
smaller are the vein-areas of the leaf. This 
difference can be seen with a hand lens by 
holding the leaves up to the light. In Vitis 
riparia, for example, accurate measurements 
of hundreds of areas in leaves picked from 
different parts of the same vine, gave an av- 
erage (vine 26 years old) area of .20398 sq. 
mm., while the largest measured .217 sq. mm. 
and the smallest .185 sq. mm. The compari- 
son for leaves from vines of different ages is 
shown by the following table, which gives 
averages from leaves picked from many plants. 
= 
4-5 Growth | 6-12 -30./ 35-5 
Rings. G. R. ESN EES 
Cuttings of V. riparia...) .44sq.mm.| .85 | .29 
Wild vines of V. riparia.| .42 33 | .24 | .16 
Even where the leaves are very large, as in 
the case of those borne on water-shoots from 
living stumps, the size of the areas is that 
characteristic of leaves borne on the tree the 
age of the stump. One of the several series of 
this kind follows: 
Tree of i 15 R., 
Castanea 8 Rings Water- 30 R. Tree 50 R. 
dentata shoot 
Size of area|.07sq.mm.|.05sq.mm. 04sq.mm./.03 sq.m. 
The results with cuttings, water shoots and 
selected vines plainly indicates that the differ- 
ence in size of areas is not due to external 
conditions. The reason that a leaf from a 
tree 25 years old differs in its venation from 
a leaf of a tree 10 years old is therefore that 
the meristematic tissue, in the two trees of the 
same species growing under the same condi- 
tions, is different. Apparently the meristem 
of the older tree produces less efficient spe- 
SCIENCE 
[N.S. Vou. XXXV. No. 898 
cialized tissues than does the younger. The 
parenchyma is less permeable, the vessels less 
efficient in conducting; the sap must be 
brought into closer contact with all the leaf 
protoplasm. Since the amount of carbohy- 
drate producing parenchyma is being gradu- 
ally decreased by the inroads of the conduct- 
ing system, the leaf is becoming a less efficient 
manufacturer of carbohydrate and ultimately 
the plant must starve. 
If the changes in the size of the vein-areas 
be plotted as a curve, the nature of the result- 
ing curve is the same as when the recognized 
senility changes in man and animals are 
plotted. It is interesting to note that changes 
in the vascular system in plants are due to the 
increasing senility of the meristem, just as 
changes in the vascular system of animals are 
due to senility. Dr. Osler says that “a man 
is as old as his arteries,” and it may be said of 
plants that they are as old as their veins. 
Since the leaves borne by cuttings showed 
but slight increase in the proportion of carbo- 
hydrate-producing tissue as compared with 
those on the original plant, it would appear 
that vegetative propagation can not and does 
not produce a young plant. The fact that the 
normal span of life for woody trees and vines 
extends in some cases over hundreds of years 
accounts for the fact that the approach of 
senility in vegetatively propagated plants is 
not more obvious. Plants which naturally 
reproduce by seed will tend to “run out” after 
long-continued vegetative propagation, ulti- 
mately dying of senility, and it is therefore 
incumbent upon our plant breeders to develop 
new varieties from seed, to take their place. 
H. M. Benepicr 
UNIVERSITY OF CINCINNATI 
THE WASHINGTON MEETING OF THE 
AMERICAN CHEMICAL SOCIETY. 
DIVISION OF INDUSTRIAL CHEMISTS AND CHEMICAL 
ENGINEERS 
G. D. Rosengarten, chairman. 
F. E. Gallagher, secretary. 
H. C. SHerman, D. A. BarrLert and N. E. 
WEATHERLESS: Relation of Ultimate Composi- - 
tion to Calorific Power in Coal. 
The analyses and calorific powers of 67 coals 
