GROWTH IN TREES. 5 



in distance between a contact rod on one side of the trunk and of one 

 end of a rod or lever on the other side is traced by a pen on the free 

 end of a lever on a sheet of paper carried by a recording cylinder. 

 Such measurements are in terms of the diameter. 



2. A dendrometer, of simple design and non-expensive construction, 

 has been perfected, which may be placed around the trunk of a tree 

 and the size of the trunk read on a dial from time to time. The 

 essential parts of this instrument are an encircling wire engaged with 

 a number of bearing levers. One end of the wire is anchored and the 

 other is attached to the short end of a lever, the free end of which moves 

 over a scale giving readings of the size of the trunk in terms of several 

 radii, or of the circumference. 



3. Dendrographic records of trees have been made as follows: 



Citrus aurantica: Citrus Experiment Station, Riverside, California; by H. S. Reed. 



Fagus grandifolia: Baltimore, Maryland; by B. E. Livingston. 



Fraxinus arizonica: Tucson, Arizona; by H. W. Fenner. 



Juglans major: Carmel, California; by D. T. MacDougal. 



Parkinsonia microphylla: Tucson, Arizona; by B. R. Bovee. 



Picea pungens: Cottonwood Nursery, Wasatch Mountains, Utah; by C. F. Korstian. 



Pinus chihuahuana: 6,000 feet altitude, Santa Catalina Mountains, Tucson, Arizona; by 



D. T. MacDougal and B. R. Bovee. 

 Pinus ponderosa: Alpine Laboratory, Pikes Peak, Colorado; by F. E. Clements and Gorm 



' Loftfield. 



Pinus radiata: Seven trees, Carmel, California; by D. T. MacDougal. 

 Pinus scopulorum Lemmon: Fort Valley Experiment Station, Flagstaff, Arizona; by G. 



A. Pearson. 



Platanus occidentalis: Missouri Botanical Garden; by B. M. Duggar and F. S. Walpert. 

 Populus deltoides': Missouri Botanical Garden, by B. M. Duggar and F. S. Walpert. 

 Populus macdougalii: Continental, Arizona; by W. B. McCallum. 

 Pseudolsuga mucronata Sudworth: Alpine Laboratory, Pikes Peak, Colorado; by F. E. 



Clements and G. Loftfield. 

 Quercus agrifolia: two trees, Carmel, California; by D. T. MacDougal. 



4. The trees noted above represented deciduous and evergreen 

 coniferous types native to the Atlantic seaboard, the Mississippi valley, 

 various elevations in the Rocky Mountains, the plateau, mountain 

 slopes, and desert valleys of Arizona, the plains of southern California, 

 and the coastal region at Carmel, with a wide variety of climatic con- 

 ditions and seasons. 



5. The period in which enlargement of trunks takes place is com- 

 paratively brief, even in places in which the season is of indeterminate 

 duration. 



6. Growth is an activity of an embryogenic tract of tissue, which 

 depends upon environmental conditions, and no part of the observa- 

 tions suggested a seasonal rhythmic action. The Chihuahua pine, 

 which exhibits growth of the trunk with that of the branches on the 

 dry mountain slopes in the advance of the temperatures in May and 

 June, is brought to rest coincident with the desiccation of the soil in 

 the dry fore-summer. Reawakening ensues consequent upon the sum- 

 mer rains, and enlargement continues until checked by the decreasing 

 temperatures and increased soil desiccation in the autumn. The 



