20 Wisconsin Academy of Sciences, Arts, and Letters. 
THE CAUSES AND THE OCCURRENCE OF EXCENTRIC RADIAL GROWTH. 
In a study of the distribution of excentric radial growth on 
trees it is well to note that excentricity may conceivably come 
about in one or more of four ways and that in a sense such an 
uneven growth of a stem at any height corresponds to the wave¬ 
like uneven distribution at different heights of a tree. The four 
ordinary ways excentric stems may be built up are (1) by the 
entire omission of radial growth in a part of the circumference, 
(2) by the unequal rate of growth on different sides of stems, 
(3) by the entire omission of summer growth on one side and, 
(4) by the omission of spring growth on a part of the cir¬ 
cumference and its occurrence at other places. In looking over 
papers on excentric stems, etc., it is sometimes difficult to deter¬ 
mine to which of the four classes the case under consideration 
belongs but usually that is apparent. 
Gravity and other factors of the environment as w 7 ell as the 
anatomic or physiologic characteristics of a species seem to be 
the causes of excentric radial growth but as yet the matter is 
not fully understood. That a difference may be found in trees 
of different groups in regard to excentric growth, when subjected 
to the same environment, is shown by some observations by 
Nbrdlinger. 34 He cites an instance in which saplings of conifers, 
beech, and oak had been bent over by the heavy snows of 1868 
and afterwards grew in slanting positions. Three years later 
sections taken at any point of the stems showed that pine, spruce, 
and larch had developed three excentric rings with the larger 
radius below while on the oaks and beeches the three last rings 
were thicker above. In one spruce only one very narrow ring 
had been laid down on the upper side while the other rings had 
been wholly omitted on that side. In both oak and beech radial 
growth had been extremely slight on the under side during the 
three years. This show^s that different trees subjected to the 
same environment may respond differently. That is, the specific 
characteristics of a plant to a certain extent determine the man¬ 
ner of response to the environment. 
Muller’s 35 observations seem to indicate that if excentric 
84 l. c. 
80 Muller, N. J. C. Beitrage zur Entwicklungseschichte der Baum- 
krone. Bot. Untersuchungen 1:512-24. 1877. Heidelberg. 
