iQiS] 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 xyleni are thin- 

 walled and easily crushed 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 (i) that sUght 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 191 2, 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 



