iQisl BROWN— PINUS STROBUS 241 



36. DeVries, H. tlber den Einfluss des Drucks auf die Ausbildung des 

 Herbstholz. Flora 55:241-246. 1872; 58:97-102. 1875. 



37. WiELEE, A., Beitr. zur Kenntnis der Jahrringbildung und des Dicken- 

 wachstums. Pringsh. Jahrbiich. 18:70-132. 1887. 



38. , Uber die Periodicitat in der Wurzelbildung der Pflanzen. Forstw. 



Centralbl. 16:333. 1894. 



39- , tJber die jahrliche Periodicitat im des Holzkorpers der Baume. 



Thar. Forstl. Jahrb. 48:39-139. 1898. 



EXPLANATION OF PLATES XIII AND XIV 



Fig. I. — Cuttinglll taken from tree I, December 22, 1912; cambium and 

 phloem in the resting condition; X75. 



Fig. 2. — Cutting I taken from tree I, February 20, 1913; phloem (A-B) 

 in winter condition; Xr6o. 



Fig. 3. — Cutting IV, same; contraction from low temperature more 

 •restricted; X160. 



Fig. 4. — Cutting I taken from tree I, April 26, 1913 ; growth taking place 

 very rapidly (c, approximate position of the cambium) ; X 100. 



Fig. 5. — Cutting II taken from tree I, May 12, 1913; rapid xylem forma- 

 tion has occurred (c, approximate position of the cambium) ; X 50. 



Fig. 6. — Cutting IV taken from tree I, September 19, 1913; transitional 

 forms of tracheids, slow growth; Xiio. 



Fig. 7. — Cutting III taken from tree I, September 26, 191 2; autumnal 

 condition of the phloem; X200. 



Fig. 8. — ^Diarch white pine root before secondary thickening; two exarch 

 bundles in process of formation; X90. 



Fig. 9. — ^Tetrarch white pine root after secondary thickening; X25. 



Fig. 10. — Same enlarged, showing 4 original xylem rays; X3S. 



Fig. II. — ^Long roots and short roots of white pine. May 10, 1913. 



Fig. 12. — ^New growth of long roots. May 14, 1913. 



