RELATION OF STIMULI TO THE CONE PRODUCTION OF 

 WESTERN HEMLOCK 



By RusselIv Watson 

 Instructor in Forestry, University of Michigan 



A fact well known to botanists is that plants which have enjoyed a 

 period of thrifty growth may often be made to reproduce if factors 

 of growth are introduced which suddenly check the rapid vegetative 

 activity. Such factors which inhibit the growth of the plant may be 

 thought of as stimuli to reproductive activity. It should not be under- 

 stood from this that because a plant is growing slowly that it is neces- 

 sarily reproducing actively; runty corn-stalks bear runty ears, and a 

 neglected orchard bears little as well as poor fruit. 



Many examples may be cited which indicate the relation between 

 abundance of food and vegetative and reproductive activity. Many 

 fungi which will not produce spores when grown on a medium abun- 

 dant in food, when grown on a medium poor in food value will often 

 bear fruiting bodies. Under certain conditions annuals may be trans- 

 formed into biennials or perennials by keeping them under conditions 

 favorable to vegetative activity, and in the same manner plants which 

 normally flower every year may be kept from flowering for several 

 years. Hydrophitic plants when grown under xerophytic conditions 

 may flower annually, although if grown under their native environ- 

 ment may flower only rarely. Such instances are common knowledge 

 to the botanist.^ 



The occurrence of the seed crops of the forest trees has long been a 

 matter of decided interest to foresters, principally, perhaps, because of 

 its importance in the practice and determination of silvicultural meth- 

 ods. A description of the silvicultural characteristics of a tree usually 

 includes, as a matter of course, a statement of the periodicity of heavy 

 crops of seed. Indicating this, the following statements are typical: 

 "Some seed is borne every year, but heavy seed years are of irregular 

 occurrence." "A prolific seeder, exceptionally heavy crops every three 

 to five years," etc. 



Yet Zon writes : "When several years ago an attempt was made bv 



*For further discussion see "Text-book of Plant Physiology," Pierce; Pfeffer's 

 'Physiology of Plants" ; MacDougall's "Text-book of Plant Physiology," etc. 



168 



