174 JOURNAL OF FORESTRY 



Fungi. — Although a number of trees were examined which were 

 badly rotted, nothing definite could be determined as to the effect of the 

 rot upon the seed production of the tree. 



The action of Razy motif skya .sp., which causes a witches-broom 

 growth on the limbs of hemlock, is toward a vegetative stimulation. 

 Unfortunately the cases of witches-broom observed were such that it 

 could not be decided whether or not this stimulation tended to inhibit 

 the production of cones. 



Mechanical Injuries. — Healthy trees which had had their tops taken 

 off in logging or snapped off by wind, or by other causes, were very 

 interesting. It was found that very often those limbs which were im- 

 mediately under the break produced very heavy crops for a year or two 

 after the accident. The trees examined, however, which had responded 

 to this stimuli bore seed not more than two years in succession after 

 the accident, and generally only one year. There is probably a relation 

 here between the response to the stimuli, the duration of the response, 

 and the rapidity with which a new leader is formed. Trees partially 

 girdled often bore heavy crops. 



An injury to the trunk immediately below a limb was often the cause 

 of the limb bearing heavily. The rubbing of one limb on another was 

 found to cause a seed production on the limbs outside the rub. Such a 

 condition was especially noticeable when, as was often found, no other 

 limb on the tree was bearing cones in abundance. This point was con- 

 sidered of great importance in deciding that external factors exercise 

 a deciding influence upon the cone production of trees. 



Trees partially wind-thrown, with some broken roots, but yet with a 

 sufficient number left to carry on life in the trees, often produce heavy 

 crops. These crops may continue for several years in succession. 



Light. — Nothing definite could be found as to the effect of light as a 

 stimulus to seed production. 



Soil and Moisture. — Nothing definite could be determined. 



Date of Injury. — On this point, unfortunately, data could not be 

 gathered. Very likely it is one of the most important factors in the 

 relation between injury and cone production. It is a matter for experi- 

 ment. 



One conversant with the facts, as are the investigators,* can scarcely 

 doubt that hemlocks are stimulated to cone production by fires, insects, 

 etc., and many conjectures based upon this fact might be made regard- 

 ing the ease of stimulation of hemlock (that is, thickness of bark) and 

 its tolerance and position in the forest. 



'J. H. Billingslea collaborated with the author during a considerable part of 

 this study. 



