1912] CURRENT LITERATURE 77 



"The maiden hair tree." The American publisher is G. P. Putnam's Sons 

 of New York. — J. M. C. 



North American Flora. 7 — Vol. VII, part 3, continues the treatment of 

 the Uredinales and contains the Aecidiaceae from Prospodium to Dichaeoma 

 by Joseph Charles Arthur, the text for the genus Gymnosporangium being 

 contributed by Frank Dunn Kern. One new genus (Argomyces) is proposed, 

 which has a geographical distribution from New Mexico and Texas through 

 Mexico and the West Indies to South America, and is represented at present 

 by four known species. Further new species are characterized in the following 

 genera: Earlea (1), Kuehneola (1), Spirechina (1), and Xenodochus (1). 



J. M. Greenman. 



NOTES FOR STUDENTS 



Variation curves. — Several years ago papers dealing with variation 

 in the number of parts of flowers, flower heads, inflorescences, etc., were of 

 frequent appearance. As the novelty of the method disappeared, the number 

 of contributors to the knowledge of such variations has decreased, but, as is 

 usually true in such cases, the value of the contributions has correspondingly 

 improved. Several recent studies in this field are of exceptional interest. 



Vogler 8 gives a large number of counts of ray flowers in Chrysanthemum, 

 Boltonia, and Senecio. In Chrysanthemum Parthenium he found a curve having 

 the mode on 21 when the plants were grown on well-manured soil, and on 13 

 when grown on infertile soil, the curves being strongly skew in each case 

 toward an intermediate point, the mean values lying between 14 and 19. 

 These results agree essentially, therefore, with those of Klebs 9 on Sedum 

 spectabile. In Boltonia latisquama the ray flowers have a wide range of varia- 

 tion (39-81), with the summit of the curve near 55. Three different plants 

 were separately counted in three successive years, and although the different 

 seasons differed considerably, there was no corresponding change in the number 

 of ray flowers. One of these plants had each year the mean number approxi- 

 mately 57, another approximately 54. These permanent differences are proba- 

 bly not to be attributed to genotypic differences in the plants, however, as they 

 originated from a common stock by vegetative division. In Senecio alpinus 

 a count of over 3000 heads from two different localities in three different years 



every 



vincing 



7 North American flora. Vol. VII, part 3, pp. 161-268. The New York 

 Botanical Garden. April 15, 1912. 



8 Vogler, P., Variation der Anzahl der Strahlbluten bei einigen Kompositen. 

 Beih. Bot. Centralbl. 25:387-396. 1910. 



9 Klebs, G., Studien iiber Variation. Arch. Entwick.-Mech. Organ. 24:29-113. 

 1907. 



