iQiS] BROWN— PINUS STROBUS 235 



of yearly elongation is lost after the first year. No attempt was 

 made to trace rapidity of growth of white pine roots. Roots from 

 the same tree on May 30 exhibited an average growth of 4-5 

 inches, but no other material was secured. We can only infer 

 from the data at hand that growth in length began as early as 

 April 26, possibly much earUer. 



The results of others in regard to the duration of root growth 

 are interesting in this connection. Resa (27), after repeated 

 observations on root growth, came to the conclusion that there are 

 in all roots two periods of root development, one in the spring, 

 which occurs mainly before the unfolding of the leaves, and a second 

 during September and October. The last persisted through the 

 winter in dicotyledons, with many interruptions from time to 

 time, but without complete cessation. In conifers, on the other 

 hand, there was a decided rest period during January and February. 

 WiELER (38) combated Resa's conclusions and maintained that 

 in the autumn, after leaf fall and the resulting lessened demand 

 for water, no new roots were necessary. Peterson (26) worked 

 with young and old trees of a number of dicotyledons, as well as 

 specimens of Picea excelsa, Pinus montana, and Larix decidua. 

 His results in every way substantiate those of Resa and contra- 

 dict the conclusions of Wieler. Among other points explained, 

 Peterson points out that there is a period of root elongation which 

 may occur in the spring anywhere between February and June. 

 In June, and especially in July, elongation gradually ceases. This 

 is followed by a reawakening in growth in length from August 

 until October and even into November. The author does not 

 state in which period growth is more intense. The researches of 

 BusGEN in 1901 (4) and Engler in 1913 (6) substantiate in every 

 way those of Resa and Peterson, so it may be concluded that 

 there are two periods of elongation, and furthermore, that in white 

 pine the first begins in late April and continues into early June or 

 even later. 



Secondary growth in underground parts 



Secondary growth in roots, as in stems, begins the first season, 

 and once started proceeds in the usual way. Mention has already 

 been made of the variabihty in white pine roots as regards the 



