28 Wisconsin Academy of Sciences, Arts, and Letters. 
were found to develop in the second and subsequent annual rings 
by the elimination of most of the wood cells between adjoining 
rays. Eames 48 has noted a similar compounding of the simple 
rays of white oaks. Rubner found that the ray cells in the val¬ 
ley wood are shorter than those in the ridge-wood. The wood 
in valleys often showed no indication of rings because the cells 
were frequently all of the summer-wood type with a reduced 
radial diameter. In the deep valleys many rings were found to 
converge into a homogeneous layer of small cells many of which 
had brownish contents. In some cases as many as twenty-two 
year’s growth had occurred on the ridges while no growth re¬ 
sulted in the valleys. In some such instances the cambium in 
the valleys had become thick-walled and apparently lost its 
power of growth and in others it had died and turned brown. 
In the smaller valleys of trunks phloem production w r as found 
excessive while on the ridges it was only slight. Rubner also de¬ 
scribed instances in which no radial growth resulted on the lower 
portion of tree-trunks during a number of years. He found 
that long branches with sparse foliage have very irregularly dis¬ 
tributed radial growth, often being wholly omitted in some por¬ 
tions and present in others, although at times with imperfectly 
differentiated cells. Similar irregularities were also noted by 
Ursprung 49 in branches of teak wood from the tropics; cross sec¬ 
tions showed that in some growing seasons the cambium had 
been active in only a part of the circumference. 
The work reviewed above shows that several types of excen- 
tric radial growth occur both in horizontal and upright struc¬ 
tures and that some of them are apparently due to differences in 
bark pressure and to an excentric distribution of the transpira- 
iton current and metabolized food, while in others the cause of 
the excentricity is not shown. For instance these authors have 
not determined why radial growth should be distributed in scat¬ 
tered patches on branches or tree-trunks which have an inade¬ 
quate supply of food or why fluted trunks and buttressed stumps 
should occur, although Detlefson made some interesting sugges¬ 
tions regarding the latter. Rubner has shown that radial 
growth is very slight in the valleys or grooves occurring in the 
48 Eames, A. J. On the origin of the broad ray in Quercus. Bot. Gaz. 
49:161-66. 1910. 
48 Ursprung, A. Zur Periodizitat des Dickenwachstums in den 
Tropen. Bot. Zeit. 62: Abt. 1:189-210. 1904. 
