stand ley: new genus of allioniaceae 629 



In the last transformation ft took the part of Q c and p of Q, 

 while n had the value — 1. 



The following observations afford an experimental illustration 

 of (36). They were made with a tube 59 em. long and 1 cm. in 

 diameter, containing a \ inch (0.635 cm.) ball, ordinarily of steel 

 (p = 7.7 g./cm. 3 ). The tube was filled with lard oil (p. = 0.74 



c. g. s. units, p = 0.92 g./cm. 3 ). The slope — was found to be 



OjJ. 



31 c. g. s. units. Substituting now a brass ball (p = 8.6 g./cm. 3 ) 

 for the steel one, the roll-time dropped from 27.9 to 24.7 seconds, 



making — equal to — 3.6 c. g. s. units. From these data, in 



Opo 



conjunction with (36), the value — = 5.2 c. g. s. units would 



Op 



be predicted. From (32), the actual value is found to be 5.7 

 c. g. s. units. Since — is itself a correction term, the agree- 



Op 



ment is sufficient. 



BOTAXY. — Ammocodon, a new genus of Allioniaceae, from the 

 southwestern United States. 1 Paul C. Stand ley, National 

 Museum. 



The genus Selinocarpus was proposed by Gray, in 1S53, 2 in a 

 paper dealing with the plants of the family Allioniaceae 3 col- 

 lected by Charles Wright during his explorations of western 

 Texas, southern Xew Mexico and Arizona, and northeastern 



1 Published by permission of the Secretary of the Smithsonian Institution. 



- Amer. Journ. Sci. II. 15: 262. 



3 Dr. Gray used the family name Xyctaginaceae. a term more widely employed 

 by botanists than the earlier Allioniaceae. The designation of this family is 

 not based, as some suppose, upon the genus Nyctaginia, but upon Nyciago, an 

 early name for the four-o'clocks, to which Linnaeus assigned the generic term 

 Mirabilis, which is universally used today. Consequently the term Xyctagi- 

 naceae is objectionable, as applied to a family, since it is based upon a generic 

 name nowhere accepted as valid. 



An example of mistaken ideas concerning the source of the word Xyctaginaceae 

 and certain related forms is found in Catalogue of the Flowering Plants and Ferns 

 of Connecticut (Connecticut Geol. and Nat. Hist. Surv. Bull. 14, p. 172. 1910). 

 In explanation of the specific name of Oxybapkus nyctagineus (Michx.) Sweet 



