50 MISSOURI BOTANICAL GARDEN. 
conditions and in different climates. All workers with 
wood recognize the fact that its strength is a very variable 
yenty and for that reason it is unsatisfactory for use in, 
avy structures, since the amount of stress which it can 
withstand is more variable than is that of steel and iron. 
There is a decided difference between a certain species 
grown on dry hills and the same species grown in moist 
lowlands. Much more then must there be a difference 
between wood of the same species when grown in essentially 
different climates. May not, in the same way, the degree 
of lignification of the walls be affected by external condi- 
tions? Potter * says, ‘local conditions of soil and climate 
seem in some cases, to retard the complete development of 
the xylem, and thus render such trees constitutionally weak 
and very liable to attack.’’ Von Schrenkt has also inti- 
mated something of a similar nature in connection with 
Fraxinus Americana when growing on the western border 
of its range. He says, ‘In the present instance it would 
seem, that there might be some relation between the greater 
susceptibility on the part of the ash near its western limit 
and its generally weaker development at thislimit. It will 
be an interesting point to determine for instance whether 
the rate with which branch wounds or stubs heal in Ohio 
and Pennsylvania is greater than in Missouri and Kansas. 
That the rate of growth is slower in the Western States we 
know.’’ In the same way may not the firmness with which 
the lignin is held in combination with the other constitu- 
ents of the wall bealso affected by the external conditions? 
This certainly does vary as is shown by the preceding 
experiment upon the spring and summer wood. 
ARRESTED DEVELOPMENT AND RESERVE STORAGE. 
The occurrence of cellulose in the form of an inner, 
* Potter, 2. ¢: 
t Von Schrenk. U. 8. Dept. Agric. Bureau of Plant Seiensy: Bull. 
$2: 11. (1908). 
2 isd J 
ee 
