126 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I40 



Thus the growth layers found in branches may be said to arrange 

 themselves in a series from completely diffuse and local to completely 

 sharp and regional within the tree. All types of growth layers and all 

 types of contacts exist among growth layers, whether annual or intra- 

 annual. 



ABSOLUTE DATING AND THE DETECTION OF MULTIPLICITY 



The whole range of growth-layer types is highly suggestive of mul- 

 tiplicity. Indeed, a close study of the gradual and complete transition 

 from interrupted lightwood, interrupted densewood, divided dense- 

 wood, and divided lightwood through the whole gamut of partial 

 growth layers to complete, entire growth layers convinces the student 

 that he is dealing with intra-annuals as well as with annuals. To think 

 that a tiny lens, one or two cells in thickness and a fraction of one 

 percent of the stem in area, can represent the total growth of a normal 

 tree for a period of one year becomes increasingly impossible as a 

 person studies cambial activity. The same feeling based on intimate 

 acquaintance with trees comes in regard to partial growth layers or 

 even entire growth layers if they contrast strikingly in volume with 

 the average growth layer of the tree. Perhaps that is why Antevs 

 (1938) was a bit skeptical of the annual character of a thin ring 

 whose volume contrasted sharply with that of neighboring rings. 



It may not be amiss to mention another facet of the subject based 

 upon general impressions and observations. Scarcely a region exists 

 which does not, for that region, experience temporary droughts dur- 

 ing the growing seasons. Vegetation responds not only to such tempo- 

 rary droughts but also to warm, wet intervals. It responds visibly; 

 for instance, beech trees shedding their leaves in central Ohio during 

 a midsummer drought ; the madroiia dropping its leaves habitually 

 during the summer along the coastal region of California; the wither- 

 ing of crops; the curling, drying, or dropping of leaves from fruit 

 and nut trees in Maryland; the ocotillo putting forth a new set of 

 leaves after each summer rainy period ; the blossoming of fruit trees 

 late in the summer in Maryland and Washington, D.C. ; the setting 

 of fruit and substantial tip growth in late summer in West Virginia ; 

 the blossoming of fruit trees and spring flowers in early September 

 in Minnesota; the swelling of buds and tip growth in Texas, not 

 only in the autumn but also during the winter ; the addition of com- 

 plete tip flushes on pines high in the Sierra of California in late sum- 

 mer; and the addition of complete tip flushes after each irrigation of 

 citrus in Arizona. These observations give a vivid impression of 

 growth flushes dependent upon the fluctuation of growth factors 



