94 Forestry Quarterly 



the roots at the time they contain the largest amount of stored 

 materials, and at the time also when the fungi are in most need of 

 food, for it immediately precedes their fruiting period. 



Thus our preconceived ideas in regard to the functions of ecto- 

 trophic mycorhiza again receive a jolt. It is to be wished, howeyer, 

 that the author had based his conclusions, as to the absorptive 

 relations of the mycorhiza, upon physiological experiments rather 

 than upon structural appearances. 



In regard to the endotrophic mycorhizas of the maples, the 

 author concludes they are sometimes symbiotic associations and 

 sometimes associations in which the fungus can only be considered 

 as an internal parasite upon the roots. 



On the Mycorhizas of Forest Trees. By W. B. McDougall. American 

 Journal of Botany. February, 1914, pp. 51-73. 



Shepard and Bailey studied the stems of 

 Length Pinus strobus. P. palustris, Tsuga canadensis 



of and Abies concolor with a view of testing the 



Tracheids wider applicability of Sanio's finding in 



Pinus sylvestris that "in the cross section 

 of a stem or branch the tracheids increase 

 in size for a certain number of annual rings until a maximum is 

 reached, after which the size remains constant." Fifty length 

 measurements in each case were made from material taken from 

 every tenth ring throughout a section 1 foot from the ground. In 

 all four species the average tracheid length increased rapidly for a 

 period varying from twenty-five years in the case of the White fir 

 to sixty years in the case of Longleaf pine ; after that it fluctuated. 

 In the Longleaf pine (230 growth rings) a maximum average tra- 

 cheid length occurred at 160 years, followed by an irregular 

 decrease in length. The White pine, fir and hemlock, aged respec- 

 tively 120, 80 and 80 years, were apparently not mature enough 

 to have reached the stage of average maximum length. Thus in no 

 case was a constant maximum length found, although in Sanio's 

 investigation this was found within the fiftieth ring. 



2. The average length of tracheids of the same annual ring at 

 various heights in a stem of Picea rubens (50 years) was also studied, 

 to a height of 30 feet from the ground. In this case the results 

 agreed with those of Sanio that "the length of the tracheids in a 

 given annual ring in the stem increases from the ground upward 



