RELATION OF STIMULI TO CONE PRODUCTION 171 



obvious stimulants, any one of which may act either singly, independ- 

 ently, or in combination with any other. In fact, the stimuli usually 

 do act in combination. Any one of these stimuli or combination of 

 them may act with greatly varying effect upon trees which differ greatly 

 in health, growth, etc. It is impossible to combine these variables and 

 give the result as a definite figure, for the reason that no one can state 

 accurately the value of the separate factors, even when in a simple 

 combination. When these factors are combined into complex combi- 

 nations, then to evaluate them separately is practically impossible. 



The result of all this is that a tendency only can be given ; this ten- 

 dency must be accepted as the fact which was to be proved. 



If this matter of a check upon the accuracy of the work be consid- 

 ered a dilemma, then probably the other horn to it would be to give the 

 complete set of notes taken on the study. This, however, is not prac- 

 ticable for lack of space. 



With these considerations in mind, the following conclusions are 

 believed to indicate the results of the investigation : 



Periodicitv of Crops. — Considering the Puget Sound region only, no 

 definite year could be decided upon as having been an especially good 

 seed year. Individual trees were commonly found which bore seed in 

 large amounts for two or three years in succession. Indeed, some hem- 

 locks bore heavy crops for at least five successive years. On the con- 

 trary, healthy, rapidly grown trees, as well as old decadent trees, were 

 found which had borne little or no seed for at least five years. In fact, 

 some trees, although healthy and growing rapidly and over fifty years 

 old, had not borne heavy crops of cones for fully fifteen years (from 

 evidences on twigs and cones on ground), if indeed they had ever borne 

 a heavy crop. 



But it should not be understood from this that there are not occa- 

 sionally exceptionally good seed years for hemlock in the Puget Sound 

 region. It is well understood that exceptionally heavy crops of seed 

 of pines appear more or less regularly. If, however, heavy crops do 

 come at more or less regular intervals, then it would appear that the 

 causes for the heavy crop must recur thus regularly. The following 

 from MacDougall indicates this: "So long as conditions favorable to 

 vegetative growth are prevalent, reproductive processes are not carried 

 on so freely as when adverse intensities of various trophic forces pre- 

 vail." This is "richly illustrated l)y the ailixities of the higher plants'* 

 (loc. cit., p. 325). This ])resent season (1917) offers an exceedingly 

 heavy crop of cones of s])ruces, cedars, hemlocks, as well as with many 

 of the hardwoods and white pine (to some extent) over a great part of 

 the Lake States pinery region. 



