1915I BROWN— PINUS STROBUS 20i 



Investigations on the roots of trees were attempted and gave 

 some results worth noting. The roots were secured from young 

 trees (about 30 years). Other root studies were made on seedhngs 

 from the nursery. A few cuttings were taken from the roots of 

 old trees where they were exposed near the base of the bole. 



Microscopical characters of the xylem 



The xylem of white pine is so well known that it is unnecessary 

 to describe it here. When contrasted with the wood of pitch 

 pine, the xylem of white pine differs in a number of anatomical 

 features. The upper and lower walls of the ray tracheids are 

 smooth as compared with the dentate ones of Pinus rigida. 

 Bordered pits occur on the tangential walls of the late wood, while 

 they are lacking apparently in pitch pine. The transition between 

 early and late wood is not so abrupt in white pine and the rings are 

 generally wider. White pine is a more thrifty tree, and the present 

 observations tend to show that it is more susceptible to changes 

 of site, soil, etc., than pitch pine. This is exceedingly important 

 from the economic standpoint. 



The roots of white pine exhibit the usual features of the roots 

 of Abietineae. Diarch, triarch, and tetrarch roots are common. 

 The root of seedlings is usually diarch (fig. 8), but the number of 

 xylem rays is as a rule soon increased to three or four.^ Vigorous 

 roots from thrifty trees between 15 and 30 years of age were pre- 

 vailingly tetrarch, so that it would appear as if the number of 

 xylem rays is correlated in some way with the amount of moisture 

 available to the root and to the root environment, whether favorable 

 or otherwise. Van Tieghem (34) has noted this same variabihty 

 in Pinus, Abies, and other alUed genera, and further has pointed 

 ' out that no constant relation prevails between the number of 

 xylem rays and the number of cotyledons. Not only does the 

 number of xylem rays vary in roots of different ages, but the 

 number may increase or decrease during the growing season. This 

 is strong evidence that environmental conditions influence within 



3 Each xylem ray is terminated centrifugally by a resin canal, and the oli- 

 garchy of young roots can in this way be easily determined in cross-section with 

 the naked eye. 



