jo Wisconsin Academy of Sciences, Arts, and Letters. 



T11K ('A l SES 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 

 a I tout 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, 

 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- 



e to which of the four classes the case under consideration 

 belongs but usually that is apparent. 



Gravity and other factors of the environment as well as the 



anatomic or physiologic characteristics of a species seem to be 



-auses 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 



Norcllinger. 34 He cites an instance in which saplings of conifers, 



beech, and oak had been bent over by the heavy snows of 1888 



p.ml 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 



thicker above. In one spruce only one very narrow ring 



-.id down on the upper side while the other rings had 



wholly omitted en that side. In both oak and beech radial 



. ' slight on the under side during the 



throt 5. This shows 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- 



;>onse to the environment. 

 ller's 35 observations seem to indicate that if excentric 



" Miiller, N. J. C. Beitrage zur Entwicklungseschichte der Baum- 

 krone. Bot. Untersuchungen 1:512-24. 1877. Heidelberg. 



