166 BOTANICAL GAZETTE [February 



mation of the daily mean temperature, above a certain fixed minimum, through- 

 out the growing season. Such indices of temperature efficiencies for plant 

 growth have been used largely by phenological students, notably in Merriam's 

 "law of temperature control." An advance upon this method was suggested 

 by Livingston, 28 based upon the supposition that growth rate may follow the 

 chemical principle of van't Hoff, doubling with each increase of temperature 

 of io° C, and the present publication proposes to give the indices a value 

 based upon physiological experiment. Lehenbauer's 29 recent experiments 

 upon the growth rate of maize seedlings at different temperatures affords data 

 for the derivation of these indices which surpass those formerly proposed 

 in taking account of the recognized principle of temperature minima, optima, 

 and maxima; and also in showing a much greater rate of increase of index 

 value with rising temperature between 2° and 32 C. Charts showing the 

 climatic zonation of the United States according to each of the 3 classes of 

 indices are suggestive and interesting for study and comparison. The third 

 method clearly surpasses the others in correctness of principles involved, and 

 its indices are used by the same author 30 in deriving a single index for 

 both temperature and moisture. As a measure of the moisture conditions, the 

 ratio of annual rainfall to annual evaporation as suggested by Transeau is 

 used, and this ratio is multiplied by the summation index of temperature effi- 

 ciency for the same period, and the product is the proposed moisture- tempera- 

 ture index. The general scheme is a good one, and the resulting zonation of the 

 United States is interesting in spite of the utter inadequacy of the evaporation 

 data. It may be doubted also whether this rainfall evaporation ratio expresses 

 the moisture conditions which determine plant growth as well as the soil 

 moisture-evaporation ratio suggested by the reviewer. It is true that here 

 again the lack of data will prevent the effective use of this ratio for years to 

 come. — Geo. D. Fuller. 



Taxonomic notes. — Collins and Howe, 31 in studying specimens of red 

 algae from Bermuda, southern Florida, and North Carolina, have recognized 

 4 new species of Halytnenia. 



Safford 32 has published Desmopsis as a new genus of Annonaceae, to 

 include 5 species from Mexico, Panama, and Costa Rica, that differ in several 

 important characters from the Old World Desmos (Unona Vahl). 



28 Livingston, B. E., Box. Gaz. 56:349-375. 1913. 



29 Lehenbauer, P. A., Growth of maize seedlings in relation to temperature. 

 Physiol. Researches 1:247-288. 1914. 



30 Livingston, B. E., A single index to represent both moisture and temperature 

 conditions as related to plants. Physiol. Researches 1 1421-440. fig. 1. 1916. 



-* 1 Collins, F. S., and Howe, M. A., Notes on species of Halytnenia. Bull. Torr. 

 Bot. Club 43:169-182. 1916. 



32 Safford, W. E., Desmopsis, a new genus of Annonaceae. Bull. Torr. Bot. 

 Club 43:183-193. pis. 7-9. fig. 1. 



