July 11, 1913] 



SCIENCE 



61 



trons are not created either out of the tung- 

 sten or out of the surrounding gas. It fol- 

 lows that they flow into the tungsten from 

 outside points of the circuit. The experi- 

 ments therefore furnish a direct experimental 

 proof of the electron theory of conduction in 

 metals. 



I wish to express my appreciation of the 

 assistance I have received from Mr. K. K. 

 Smith, instructor in the laboratory, in the 

 preparation of the tubes and in carrying out 

 some of the measurements. Mr. Smith and 

 I are engaged in a more detailed quantitative 

 study of the emission of electrons from tung- 

 sten, the results of which we hope shortly to 

 publish. I also wish to thank Dr. W. E. 

 Whitney and Dr. I. Langmuir, of the General 

 Electric Company, both for supplying the 

 specimens of ductile tungsten used and also 

 for giving me the benefit of their invaluable 

 experience. 



O. W. ElCHAEDSON 



Palmek Physical Laboratory, 

 Princeton, N. J. 



MENDELIAN INHERITANCE OF EPIDERMAL CHAR- 

 ACTERS IN THE FRUIT OF CUCUMIS SATIVUS 



The fruits of the White Spine cucumber 

 (Cucumis sativus) possess numerous white 

 epidermal spines or trichomes which roughen 

 the skin very markedly; while those of the 

 Richard's Invincible, an English forcing 

 type (var. Anglica), possess but few, small, 

 indistinct, early-deciduous and black spines 

 that scarcely roughen the skin. By crossing 

 these varieties, the White Spine having been 

 used as the maternal parent, there was ob- 

 tained a type of fruit apparently intermediate 

 in size and in number and prominence of the 

 spines, with the exception that all the spines 

 were black like the paternal parent. In the 

 F, generation, of the twenty plants grown 

 fifteen bore black spines and five white spines ; 

 six possessed smooth skins with indistinct 

 spines like the Richard's Invincible and the 

 remainder skins with various degrees of 

 roughness — a few even surpassing the White 

 Spine in the number of spines. . No correlation 

 of color of spines and roughness was noted — 



smooth-skinned progeny possessing white as 

 well as black spines. 



The inheritance of the color of the spines 

 apparently follows the simple Mendelian seg- 

 regation, although the number of progeny is 

 too small for a very exact interpretation; the 

 small number of smooth-skinned types also 

 indicates this character as a recessive one, 

 especially as the Fj fruits show no evidence 

 of this character. Practically, these data are 

 of little value unless they indicate that by 

 crossing back one of these smooth-skinned, 

 white-spined fruits with an English variety, it 

 would be possible to obtain a new white- 

 spined variety, differing in appearance but 

 slightly from var. Anglica; theoretically, it 

 adds a little more evidence to the support o£ 

 Mendel's imiversal law. 



Richard Wellington 



New York Agricultural 

 Experiment Station, 

 Geneva, N. T. 



powdery scab of potatoes in the united 



STATES 



In a recent number of Phytopathology Pro- 

 fessor H. T. Giissow, of Canada, Dominion 

 Botanist, reported for the first time in Amer- 

 ica the occurrence of the well-known Euro- 

 pean " powdery " or " corky " scab of potatoes.' 

 The specimens upon which he based this re- 

 port were received first from Quebec, where 

 the disease appeared to be well established in 

 some counties. It was also recorded in iso- 

 lated cases in widely separated regions of 

 Canada, namely. Cape Breton, Nova Scotia, 

 New Brunswick, Ontario and Alberta. These 

 facts led Professor Giissow to suggest that 

 probably the disease occurs in the United 

 States. 



In connection with certain studies now be- 

 ing carried on in the writer's laboratory upon 

 the general subject of potato scab, requests for 

 specimens of scabby tubers have been sent to 

 many individuals representing widely sepa- 

 rated localities in the state of Maine and also 



' Giissow, H. T., ' ' Powdery Scab of Potatoes, 

 Spo7igospora subterranea (Wallr.) Johns.," Phy- 

 topathology, 3: 18-19, 1913. 



