5 28 BOTAXICAL GAZETTE [june 



the tropical African flora, as illustrated by this family. In 1868, the date of 



if tropical Afi 



species 



and 170 species recorded, and at present 27 genera are known. In the present 



limits 



ferred. New species are also described in Artabotrys, Isolona, Oxymitra (3), 

 Uvaria, and Xylopia. 



Wernham 20 has published a new genus (Pseudomussaenda) of Rubiaceae 

 from the " Nile-land districts " of tropical Africa. It includes 3 species formerly 

 referred to Mussaenda, to which a new species is added.— J. M. C. 



Extraction of sap. 



Harris 



extended the work of Dixon and Atkins on the extraction of sap from plant 

 tissues. Their primary purpose was to determine something concerning the 

 nature, amount, and regularity of the change in the concentration of the sap 

 extracted from a mass of tissue under continuous pressure. The results secured 

 fully substantiate the conclusions of Ddcon and Atkins that samples of sap 

 pressed from unfrozen tissues cannot be taken as typical of the original con- 

 centration of the juices in the tissues. In general, successive samples extracted 

 by continuous pressing become more concentrated. The authors have shown 

 that such, however, is not always the case. In some instances the fluid may 

 become less and less concentrated, for example, extractions from cabbage 

 leaves. In other instances all fractions may be about the same in concentra- 

 tion. The development of the freezing method to render tissues permeable 

 and thereby obtain typical samples of sap has marked a great advance in the 

 study of the properties of vegetable saps.— Chas. O. Appleman. 



A new soil constituent.— An unusual organic soil constituent has been 

 isolated and identified as a-crotonic acid by Walters and Wise." This 

 unsaturated acid was found associated with infertility in a Texas soil where 

 drainage is poor, basic compounds deficient, and oxidizing power low. The 

 physical and chemical properties of the purified soil acid agree with the proper- 

 ties of the synthetic acid. The occurrence of this acid in nature had not been 

 certainly established previously. The authors suggest that it may be formed 

 from aliphatic /3-hydroxy acids which are produced during the destruction of 

 cellulose, or by hydrolysis of allyl cyanid which occurs in the essential oils of 

 some plants.— Charles A. Shull. 



20 



Werxham, H. F., Pseudomussaenda, a new genus of Rubiaceae. Jour. Botany 



54:297-301. 1916. 



21 



RENCE 



extraction of sap from plant tissues by pressure. Biochem. Bull. 5: 130-141. 1916. 



■ Walters, E. H., and Wise, Louis E., a-Crotonic acid, a soil constituent. 

 Jour. Agric. Research 6:1043-1045. 1916. 



