CONTENTS. 



I. 1. Revision of the Genus Tridax. 



2. Synopsis of the Mexican and Central American Species of the 



Genus Mikania. 



3. Revision of the Genus Zinnia. 



4. Revision of the Mexican and Central American Species of the 



Genus Galea. 



5. A Provisional Key to the Species of Porophyllum ranging 



North of the Isthmus of Panama. 



6. Descriptions of New and little known Phanerogams, chiefly 



from Oaxaca. By B. L. Robinsox and J. M. Gkeenmax 1 



II. A Revision of the Atomic, JYeight of Magnesium. By Theo- 



dore William Richar:^s axd Harry George Parker 53 



III. On the Group of real Linear Transformations whose Invariant is 



a real Quadratic Form. By Henry Taber 75 



IV. Studies in Morphogenesis, VI. A Contribution to the Quantitative 



Study of Correlated Variation and the Comparative Variability 



of the Sexes. By C. B. Davenport and C. Bullard . 85 



V. On the Butanes and Octanes in American Petroleum. By 



Charles F. Mabery and Edward J. Hudson ... 99 



VI. The Constituents of Pennsylvania, Ohio, and Canadian Petroleum 



between 150° and 220°. By Charles F. Mabery ... 119 



VII. Refractive Power of the Hydrocarbons and Chlorine Derivatives 

 described in the Preceding Paper. By Charles F. INIa- 



BERY AND EdWARD J. HuDSON 177 



VIII. On the Composition of a South American Petroleum. By Charles 



F. Mabery and Arthur S. Kittelberger . . . 183 



