136 ECOLOGY, PLANT GEOGRAPHY [Box. Absts., Vol. VIII, 



trees, some over 2000 years old, were used as a basis for the study. Yellow pine (Pinus 

 ponderosa) from Arizona and sequoia {Sequoia giganiea) from the Californian high Sierras 

 furnished most of the specimens, although a considerable collection of chiefly Scotch pine 

 (Pinus silvestris) with some spruce (Picea excelsa) was made in the Baltic drainage district 

 of northern Europe, a smaller collection of hemlock {Tsuga canadensis) in Vermont, and 

 another of Douglas fir {Pseudotsuga rmicronata) in Oregon. Variations in the annual rings 

 of individual trees, which in many cases were a number of miles apart, were often so uniform 

 and characteristic that they permitted ready cross-identification. The fluctuations in growth 

 reflected the sun-spot cycle or its multiples and the correlation with rainfall and temperature 

 was shown to be close over the entire range of existing meteorological data. The corre- 

 spondence of maxima and minima of these climatic variables with those of sun-spots indicates 

 a physical connection between solar activity and terrestrial weather. Although the study 

 of cycles is not considered complete the following conspicuous periods seem to be evident 

 in the rates of growth: A half, a full, a double, a triple, and a triple triple sun-spot period — 

 the sun-spot period being 10-13 years. Although these frequencies of maxima and minima 

 in the growth curves are common to all the trees, the positions are sometimes regularly dis- 

 placed, as, for example, in the Vermont trees in which the maximum growth regularly ante- 

 dated the sun-spot maximum by about 3 years. In addition, the curves of tree growth exhibit 

 a complex combination of short periods, including a prominent cycle of about 2 years; other 

 persistent cycles recur in periods of 19, 14, 10, and 7 years. It was found that the trees' year 

 begins in autumn and that double rings are indicative of spring drought. In dry climates 

 the thickness of a ring is proportional to the rainfall with an accuracy of 70 per cent and a 

 still closer correspondence may be expressed by an empirical formula that takes into account 

 the distribution of the effect of rain.over several adjoining years. For the discussion of curve- 

 smoothing, identification of rings, dating of rings, curve standardization for the decreasing 

 rate of growth with increasing age of trees, and the methods of tree selection the original 

 must be consulted. An instrument (the automatic optical periodograph) was devised to 

 reduce the influence of individual judgment in the determination of periodic changes in the 

 growth rate. With it data may be examined for periodicity of any frequency and decisive 

 conclusions drawn concerning changes in periods, recurrence of periods, and constancy of 

 period length. Its description and directions for use cannot be abstracted. — H. E. Pulling. 



944. Fuller, George D. Sap concentration in epiphytes. [Rev. of: (1) Harris, J. 

 Arthur. On the osmotic concentration of the tissue fluids of desert Loranthaceae. Mem. 

 Torrey Bot. Club 17: 307-315. 1918 (see Bot. Absts. 1, Entry 684, 828). (2) Harris, J. 

 Arthur. On the osmotic concentration of the tissue fluids of phanerogamic epiphytes. Amer, 

 .Jour Bot. 5: 490-506. 1918 (see Bot. Absts. 1, Entry 829; 8, Entry 942).] Bot. Gaz. 67: 

 374-375. 1919. 



945. Gardner, Max W. The mode of dissemination of fungus and bacterial diseases of 

 plants. Rept. Michigan Acad. Sci. 20 : 357-423. 1918.— See Bot. Absts. 3, Entry 764. 



946. JoNE.s, Frank Morton. Another pitcher-plant insect (Diptera, Sciarinae). En- 

 tomol. News 31: 91-94. 1920.— Description of a new fly, to which attention was first called 

 in 1909 by Macparlane. Other flies found in pitchers of different species of Sarracenia 

 are mentioned. — 0. A. Stevens. 



947. Miller, David. A new fungus-gnat which fertilizes Corysanthes oblonga Hook. 

 New Zealand Jour. Sci. and Tech. 1 : 4. 1918.— The gnat is Exechia thomsoni.—H. C. Cowles. 



948. Uphof, J. C. Th. Cold-resistance as an ecological factor in the geographical distri- 

 bution of cacti. Jour. Ecol. 8: 41-53. PL, 6 fig. 1920.— From observations in the desert 

 regions of Arizona and from experiments in the laboratory the conclusion is reached that the 

 protoplasm of different species offers different degrees of resistance to low temperature and 

 that this resistance is a hereditary physiological characteristic of the species. The tempera- 

 ture which damages a plant will kill it if continued long enough.— Some species have a rela- 



