March 10, 1916] 



SCIENCE 



363 



again after four iveeks, irhen cultures were dis- 

 continued. New cultures were started every two 

 weeks. The plaat here is regarded as a self -inte- 

 grating instrument set at zero of its scale at be- 

 ginning of each four-week exposure period, and 

 the integrations of climatic eiSciency for plant 

 growth are read in terms of plant measurements 

 after two and after four weeks, when the instru- 

 ments are again set at zero. The value of the 

 climate for any two-week or four-week period at 

 any station may be compared with that for any 

 other period, either at the same or at another 

 station. 



The Daily March of Transpiring Foioer as Indi- 

 cated by the Porometer and iy Standardized 

 Hygrometric Paper: Sam F. Tkelease and 

 BuKTON E. Livingston. 



The transpiring power was determined for the 

 lower surfaces of Zeirina leaves at intervals 

 throughout day and night, by method of stand- 

 ardized cobalt chloride paper. At the same inter- 

 vals porometer readings were made. If porometer 

 rates are proportional to average cross-sectional 

 area of stomatal pores, then stomatal diffusive ca- 

 pacity (Brown and Escombe) should be propor- 

 tional to square root of porometer rate at any 

 time. Graphs of this dififusive capacity and of 

 transpiring power were made for the same periods. 

 Both graphs agree in showing the same kind of 

 daily march ; values of both indices rise to maximum 

 in day and fall to minimum in night. But the 

 range of variation between minimum and maxi- 

 mum values is generally somewhat greater for in- 

 dices of diffusive capacity. It appears that 

 porometer rates do furnish data for deriving sto- 

 matal diffusive capacity in this case, but that this 

 capacity is not quite proportional to transpiring 

 power; transpiring power is here mainly depend- 

 ent upon degree of stomatal opening, but other 

 conditions are influential. If the index of trans- 

 piring power for each determination be divided by 

 the corresponding square root of the porometer 

 rate, a value is obtained that appears to be ap- 

 proximately proportional to the non-stomatal in- 

 fluence upon transpiring power. 

 The Transpiring Power of Plants as Influenced 

 by Differences of Altitude and Habitat: 

 Forrest Shrevb. 



Measurements of the transpiring power of the 

 leaves of some twenty species of plants were made 

 in the Desert and Encinal regions of the Santa 

 Catalina Mountains in southern Arizona in the arid 

 foresummer of 1915. The method of standardized 



hygrometric paper was used on the plants in 

 their natural habitats. The species investigated 

 belonged to various life-forms. They differed 

 both in the values of their transpiring power and 

 in the character of its daily changes. The same 

 species exhibits a higher transpiring power in the 

 individuals which grow in flood plains than 'n 

 those which grow on arid slopes. The daily 

 changes in the former individuals are concordant 

 with the daily march of evaporation; while in 

 the latter case the transpiring power falls sharply 

 before the daily maximum of evaporation is 

 reached. A comparison of the transpiring power 

 of the same species at different elevations has 

 shown that the daily check is applied earlier in 

 the day at lower elevations and later at higher 

 ones. The cheek is manifested, for example, in 

 Emory oak at 5,000 feet, but is in abeyance at 

 6,000 feet, where the maximum transpiring power 

 and maximum evaporation are simultaneous. In 

 the mesquite the check is applied earlier on tlie 

 desert at 2,500 feet, later at 4,200 feet and at 

 5,000 feet, but is not eliminated at the upper 

 limit of the species at the last-named elevation. 

 The values for the transpiring power are in all 

 eases higher at lower elevations, but at the higher 

 elevations the values, although not so high, are 

 sustained through a longer portion of the day. 

 Cultures of Uredineae in 1915: J. 0. Arthur. 



The report upon rust cultures for the season of 

 1915 makes the fourteenth covering consecutive 

 work, which was begun in 1899. An interesting 

 observation on the production of the alternate 

 stage of rye rust upon Anchusa is given. Aecia 

 of Puccinia Seymouriana on Spartina, heretofore 

 only known upon Cephalanthus, were grown upon 

 hosts representing two additional families. Another 

 species of Puccinia on Spartina of limited distri- 

 bution in the northwest is shown to be the corre- 

 lated form of Uromyces Spartinae, and from the 

 southwest a species of Uromyces on wild Hordeum 

 is conversely found to be the correlated form of 

 the common barley rust, Puccinia Bordei, thus 

 adding further proof of the essential identity of 

 the genera Uromyces and Pucoinia. Puccinia 

 Eriophori Thiim., in both its aeeial and its telial 

 forms, is established as a widespread American 

 species. Altogether about twenty successful cul- 

 tures were obtained, supplying various items of 

 information, partly confirmatory and partly new. 

 The Injurious Effect of Tarvia Fumes on Vege- 

 tation: A. H. Chivers. 

 An account is given of the destruction of a gar- 



