1915] -  BROWN—PINUS STROBUS 199 
also followed this method and made many consecutive borings on 
coniferous and broad-leaved trees. His observations led him to 
infer that growth is very irregular not only as between different 
trees, but at different places in the same tree. The last named 
method, however, is subject to errors, and the results of WIELER 
show wherein it is inaccurate. When a boring is made with 
Pressler’s increment borer, it is impossible to avoid applying some 
pressure to the wood core which is to be removed. During rapid 
growth (fig. 4) the elements of the newly formed xylem are thin- 
walled and easily crushéd and displaced by pressure, however 
slight. The partially formed ring when treated in this manner 
may easily show a wide variability in diameter and thus lead to 
grossly erroneous results. This appears in part to explain why 
WIELER inferred that in neighboring areas growth varies consider- 
ably. I have already pointed out (1) that slight differences occur 
in neighboring areas, and the present investigation leads to the 
same conclusion, but the marked discrepancies in growth which 
WIELER describes are not present in either of the pines which have 
been examined. 
Histological technique 
The methods pursued were in general those followed in 1910. 
The technique, however, has been improved as the time and place 
to secure the best material became more evident with increasing 
experience. The chief objection is that it is necessary to make 
rather large wounds on the trees. This objection is not so serious, 
however, in coniferous trees because the resin which exudes prevents 
quite efficiently the drying out of the tissues. 
The investigations on white pine began in August 1912, and 
continued until October 1913. Incisions were made on trees at 
intervals from base to crown (as high as it was safe to go in tall 
trees). Unless otherwise stated, these were always on the south 
Side of the tree. A few cuttings were made on the north side for 
comparative purposes. Cuttings from branches at intervals were 
also made, and, unless stated otherwise, were lateral on the branch. 
Each cutting included all or a portion of the inner bark, the cam- 
bium, and all of the preceding year’s ring except toward the end 
