586 



SCIENCE 



[N. S. Vol. XXXI. No. 798 



same for the dry steppes of the northern and 

 middle Kalahari region in South Africa. The 

 contrast between the two regions covered by 

 these two Heften is most striking. The il- 

 lustrations continue to maintain the high 

 standard of excellence which they have shown 

 from the beginning of the series. 



Professor Hansen's bulletin on " The Wild 

 Alfalfas and Clovers of Siberia, with a Per- 

 spective View of the AHaKas of the World" 

 (Bull. 150, Bureau of Plant Industry, U. S. 

 Department of Agriculture) tells, first, of his 

 several journeys into parts of Siberia, and 

 then discusses quite particularly three Siber- 

 ian alfalfas, viz., Medicago falcata, M. plaiy- 

 carpa and M. ruthenica, all of which are cul- 

 tivated. Common alfalfa, M. sativa, and sand 

 lucerne, M. media, are grown also, as are M. 

 glutinosa and M. arborea (often 10 feet high) 

 to a very limited extent. 



Professor Gates attempts to make an ana- 

 lytical key to some of the segregates of 

 Oenothera (Twentieth Annual Report of Mo. 

 Bot. Garden), and succeeds in designating no 

 less than twenty-two " species," beginning 

 with Oenothera hiennis of Linnaeus. The au- 

 thor finds it necessary to add one new species, 

 0. rubricalyx which " originated as a mutant 

 from 0. rubrinervis two years ago." Surely 

 we are making progress in regard to a prac- 

 tical acceptance of evolution! 



" Some Unsolved Problems of the Prairies " 

 are discussed, by Professor H. A. Gleason, in 

 the Torrey Bulletin for June, 1909. He con- 

 fines himself to the Illinois prairies where they 

 " were converted into cornfields long before the 

 development of ecology and phytogeography 

 in America, thus forever prohibiting the sat- 

 isfactory investigation of some questions of 

 the most absorbing interest." The sources of 

 information still available are enumerated, 

 and then he discusses eight problems which 

 have hitherto remained unsolved. 



Allied to the last is Professor C. H. Shaw's 

 paper on " Present Problems in Plant Ecol- 

 ogy" in the American Naturalist for July, 

 1909, dealing very largely with those problems 

 that develop in the study of alpine vegetation, 

 including heat, precipitation, length of sea- 

 son, light and evaporation. Little more is at- 



tempted than the setting forth of the prob- 

 lems in a distinct form. At the close the 

 author expresses the wish which every botanist 

 will echo, " that some one whose knowledge 

 of physics and physiology fits him for such a 

 task should overhaul and scrutinize our ideas 

 and methods," and a little later says " there 

 can be no question that ecology at the pres- 

 ent time contains not a little of discernible 

 error." And to the latter there is a chorus of 

 " amens " from scientific botanists every- 

 where. 



The same author shows (in Plant World, 

 August, 1909) that " timber-line " on high 

 mountains is often due to the action of the 

 snow. 



Charles E. Besset 



The University of Nebraska 



SPECIAL ARTICLES 



ARTIFICIAL PRODUCTION OP MDLTIVOLTINE RACES 

 OF SILKWORMS 



The domesticated moths known as silkworms 

 have been the subject of much interesting ob- 

 servation and experiment in recent years. The 

 work of Toyama,^ Coutagne'' and particularly 

 that of Kellogg'' in this country, has added 

 much to our knowledge of the hereditary proc- 

 esses revealed by the manifold varieties of this 

 insect. In a recent study Miss McCracken,* 

 continuing the previous work in Professor 

 Kellogg's laboratory, has studied the heredity 

 of the race characters, bivoltism and univolt- 

 ism, in the silkworm. By the former term is 

 meant the condition by virtue of which two 

 broods are produced annually, whereas in the 

 univoltine form, but one brood is reared, the 

 eggs laid in the spring wintering over and 

 hatching out the following spring. This 

 racial character being a physiological rather 

 than a morphological one, is of peculiar in- 

 terest in heredity. 



The elaborate breeding experiments of Miss 



^ Bull. Agricultural Coll., Tokyo Imp. Univ., 

 VII., 1906. 



""Bull. Solent, de la France, XXXVII., 1903. 



" " Inheritance in Silkworms," L. S. Jr. Univ. 

 Pui., 1908. 



" Jour. Exp. Zool., 1909, VII., 747. 



