62 Wisconsin Academy of Sciences, Arts, and Letters. 



only about 27 cm. high in January and their stems about 21 mm. 

 in circumference, while those in four liter pots were about 90 

 cm. high and 50 mm. in circumference. Those transplanted to 

 the field became large plants with woody stems. Five dwarfed 

 plants, which were subsequently transplanted to a forcing bed, 

 had since made a rank growth and were retransplanted to four 

 liter pots. They wilted but eventually recovered their turgid- 

 ity, although the older leaves died. 



Cross sections showed the xylem cells of the field plants 

 to be larger and the vessels more numerous than in those re- 

 tained in the small pots. In the plants transplanted to the field 

 the xylem cells around the pith were small and were surrounded 

 by larger ones toward the periphery. In case of those trans- 

 planted to four liter pots the same inversion of the normal po- 

 sition of large and small celled xylem occurred, but in addition 

 the outermost rows again had a much reduced radial diameter. 

 In the field plants which had been retransplanted to pots the 

 outermost cells also had a reduced radial diameter and thick 

 walls while within them was a zone of large, thin-walled cells 

 which had apparently been formed just before the last trans- 

 planting and as a result their walls remained unthickened. 

 Similar results were also obtained with Helianthus annuus. 

 Wieler concluded from these experiments that the abundant 

 supply of metabolized food to the cambium is the most important 

 factor in the production of spring wood and that the shortage 

 of such a food supply induces the formation of summer wood, 

 and that therefore "annual" rings of trees are due to an abun- 

 dant supply of organic food to the cambium in spring and a 

 reduced supply in summer. 



Lutz 124 was of the opinion that when the food supply to a 

 rapidly dividing cambium is comparatively low while water is 

 abundant the cells become large and thin-walled as is charac- 

 teristic of spring wood, while if the food supply is good and the 

 water is low the cells become small and thick-walled as in sum- 

 mer wood. 



In a later paper Wieler 125 reiterated his former conclusions 

 though he admits his inability to prove that the small radial 



121 l. c. 



126 Wieler, A. TJeber die Abhangigkeit der Jahresringbildung von den 

 Ernahrungsverhaltnissen. Aligem. Forst-u. Jagd-Zeit. 67: 82-89. 1891. 



