422 



BOTANICAL GAZETTE 



[may 



northern Maine, 2 from Utah and Nevada, and 1 from Mexico. In addition 

 to the full descriptions and synonymy, the citations of stations and exsiccatae 

 are very complete. 



Griffiths 15 has described 9 new species of Opuntia, which have been grow- 

 ing under his observation for 5-8 years. 



Pittier 16 has published a revision of Inga, a large American genus of 

 leguminous trees, which has not been revised since 1875. He recognizes 212 

 species, 40 of which are new, representing 5 sections, which are further sub- 

 divided into series. 



Rendle 17 has published Maidenia as a new genus of Hydrocharidaceae 



from West Australia. It is a delicate water plant 5-6 cm. high, covered with 

 numerous threadlike leaves, and belongs to the Vallisnerieae. 



Werxham, 18 in a seventh paper on the Rubiaceae of the American tropics, 

 has published an analytical key to the genera. The extensive display of 

 Rubiaceae in this region is indicated by the fact that 182 genera are recognized, 

 distributed among 21 tribes. 



Wright 19 has published a new genus (Thuranthos) of Liliaceae from South 

 Africa, related to Drimia Jacq. — J. M. C. 



Excretion of acids by roots. — Haas 20 has taken up the much controverted 

 question, do roots give off acids other than carbonic ? He grew roots of early 

 sweet corn in distilled water for 5 and for 19 days and tested the H+ concen- 

 tration of the water against standard buffer solutions of phosphates with 

 phenolphthalein as the indicator. He concludes that no acid other than 

 carbonic is excreted by roots, but that decay of the roots does give a slight 

 increase in the alkalinity of the water. The author says "The problem is 

 important not only because acids dissolve plant food from the soil, but also 

 because it involves the fundamental questions of the reaction of protoplasm 

 and of the mechanism of excretion. " This is true, but to answer the question 



in a way applicable to natural conditions one should not put them in the 

 abnormal conditions offered by distilled water. 21 One might also expect the 



** Griffiths, David, Additional species of Opiuitia. Bull. Torr. Bot. Club 43 • 

 523~53L Pi- 30. 1916. 



16 Pittier, Henry, Preliminary revision of the genus Inga. Contrib. U.S. Nat. 

 Herb. 18:173-223. pis. 81-10$. 1916. 



* 



,7 Rexdle, A.B., A new genus of Hydrocharidaceae. Jour. Botany S4'3 l 3~3 l6 ' 

 pi. 545. 19 16. 



18 Werxham, H. F., Tropical American Rubiaceae. VII. Jour. Botany 54- 

 322-334. 1916. 



x » Wright, C. H., Diagnoses Africanae. LXIX. Kew Bull. 1916-.no. 9. p. 233. 



20 Haas, A. R., The excretion of acids by roots. Proc. Nat. x\cad. Sci. 2 : 561-566. 

 1916. 



* 



21 True, R. H., The harmful action of distilled water. Amer. Jour. Bot. 1 : 255- 

 273- fii- i- I 9H- 



