June 6, 1913] 



SCIENCE 



883 



feet than during other parts of the molting 

 cycle. 



The more gradual molts may also afEect the 

 rheotactic reaction. A cut of 20 per cent, in 

 the positive response has been observed when 

 one segment was molted. Regulation from 

 depressed to normal positiveness occurs more 

 rapidly after' a molt than at any other time. 



The detailed account just given shows that 

 the effect of the molting period lasted for 

 about five hours after the actual ecdysis took 

 place. If the period extended as long before- 

 hand it would make the time during which 

 the rheotactic response is affected by the molt- 

 ing process extend over a period of ten hours. 

 Since both the rheotactic and thigmotactic 

 responses are weakened, this must be a critical 

 time in the life of the stream isopod. 



W. C. Allee 



A NEVADA RECORD FOR THE CAXADA OTTER, 

 LUTRA CANADENSIS (SCHREBER) 



No otter has apparently been known from 

 Nevada, although Lutra canadensis is known 

 to occur in Idaho, and the type specimen of L. 

 canadensis sonora (Rhoads) was taken at 

 Montezuma Well. Yavapai County, Arizona. 

 The Walker-Newoomb Expedition of the Uni- 

 versity of Michigan, in the summer of 1912, 

 found a species common on the Humboldt 

 River in the vicinity of Elko and Carlin, in 

 the northeastern part of the state, and from a 

 trapper a specimen was secured for the Mu- 

 seum of Zoology (Cat. No. 44,419). 



The specimen obtained, a large adult male, 

 is evidently to be referred to L. canadensis, as 

 at present defined. The coloration is not as 

 pale as described for L. c. sonora, being dark 

 liver-brown above and paler below, the cheeks, 

 lips, chin and throat whitish; and the post- 

 orbital processes are not attenuated, as in L. 

 c. sonora, but short and stout, as in typical L. 

 canadensis. 



Alexander G. Ruthven, 

 Frederick M. Gaige 



SOCIETIES AND ACADEMIES 



THE botanical SOCIETY OF WASHINGTON 



The eighty-seventh regular meeting of the Bo- 

 tanical Society of Washington was held at the 

 Hotel Cochran, February 25, 1913. This was the 



regular annual opening meeting of the society, 

 Fifty members and forty-two guests were present, 



The retiring president, Mr. W. A. Orton, de 

 livered an address entitled ' ' Environmental Influ 

 enees in the Pathology of Solanum tuberosum.' 

 This paper was published in the Journal of the 

 Washingten Academy of Sciences (Vol. 3, p. 180, 

 April 4, 1913). 



The eighty-eighth regular meeting was held in 

 Assembly Hall, Cosmos Club, Tuesday evening, 

 April 1, 1913. 



Mr. James T. Jardine was elected to member- 

 ship. 



The following papers were presented : 



Notes on Disea.ses of Trees caused by Mistletoes : 



Dr. G. G. Hedgcock. 



Mistletoes are found only on conifers in north- 

 ern and northeastern United States; only on an- 

 giosperms in southeastern and southern portions; 

 and on both in western and southwestern regions, 

 where they are the most widely disseminated. 



The rate of spread of mistletoes is without 

 doubt very slow. Near Frazer, Colorado, on an 

 old burn in the forest, the rate of spread of 

 Eazov.mofs'kya americana (Nutt.) Kuntze on the 

 lodge pole pines (Finns contorta Lond.) is esti- 

 mated to be from 6 to 12 feet per annum, where 

 mechanical expulsion of the seeds aided by winds 

 are the controlling factors. Sporadic infections 

 at much greater distances are caused possibly by 

 birds or animals. 



Light is the most important factor in determin- 

 ing the spread of mistletoes of species of both 

 BasoumofsJcya and FJtoradendron. Trees in the 

 open, and in more exposed conditions, whether on 

 ridges or edges of canyons or on level areas are 

 most subject to attacks by mistletoes of both 

 genera on account of the abundance of light. 

 Trees in dense forests are not subject to attack. 

 Mistletoes are stunted by dense shade, and bear 

 but few, if any seeds, and can not well maintain 

 themselves under conditions where the light is 

 deficient. 



One of the immediate effects of the presence of 

 the sinkers of these parasites in the tissues of host 

 trees and shrubs is a tendency to hypertrophy in 

 the immediate region of penetration. In ease of 

 species of Phcradendron, unless the mistletoe plant 

 is broken off there is little or no tendency for its 

 sinkers to spread laterally in the tissues of the 

 host, and when broken off, the rate of spread is 

 slow, and no witches brooms are formed. In case 

 of species of BasoumofsJcya, witches brooms are 

 commonly produced. The lateral sinkers in such 

 cases spread in the soft tissues of the host, keeping 



