56 



of dodder — ^that is, they prescribe certain grades of purity for imported 

 seed ; and precisely for this reason, it -would be of the greatest importance 

 to know the limits within which dodder exercises its damaging effect. 



Thus, the growers of fodder, the merchants and the Seed Control Stations 

 have a common interest in determining these limits. I believe I do not 

 err in assumiing that a similar interest in this question also exists in America 

 and that interest in it will also arise in Asia. 



In view of the importance of the question, I must regret how relatively 

 small is the interest evinced in the work of the Dodder Committee. 

 This may perhaps be due to the fact that the solution of the question 

 is sought during a period when the political and financial confiosion in East 

 and Middle Europe has greatly increased the difficulties of such work. 



With Russia, a country which, in respect to dodder, is of peculiar 

 interest and ha*, according to supposition, a limit of noxious effect 

 stretching across the country from West to East, we were unable to estab- 

 lish contact. 



From Germany, with its mosaic of districts differing in climatic 

 character, we could obtain no positive information, obviously in consequence 

 of the political confusion which has prevailed there in recent years. All 

 the efforts which Professor Voigt devoted to investigation Were unavailing. 



In France, according to Professor Bussard's report, there is no limit 

 for the common dodder (Cuscuta Trifolii), this weed being met with in 

 all parts of the country; on the other hand, the large-seeded dodder 

 (Cuscuta racemosa or suaveolens) is limited to certain districts Which are 

 greater or smaller in number according to the climatic conditions pre- 

 vailing in any particular year, and as these districts are distributed 

 irregularly, it is very difficult to determine their boundaries. According 

 to Professor Bussard, more extensive research would be required to 

 establish the limits of dodder growth in France. 



From Roumania I have received no data. I have informed Director 

 Enescu of our system of question sheets for ascertaining the limits of 

 dodder effects, but hitherto I have received no reply. 



From Czecho- Slovakia also there are no data, for I have not succeeded 

 in establishing correspondence with Director Vitek. 



The most important details I have received exhibiting the correct method 

 of procedure in this question, came from Dr. A. Volkart, of Switzerland. In 

 Switzerland, on the north side of the Alps, only the common dodder (C. 

 Trifolii) plays any sort of role, and here also, according to the observations 

 made, the growth appears with injurious effect only Within the rainfall 

 curve of 1,000 mm. In districts with a greater rainfall, the growth is not 

 injurious. In warm, dry years the dodder does more damage and also 

 develops many ripe seeds, which again infect the soil for a series of years : 

 in wet years the damage is of small extent. 



Nevertheless, there are to be found everywhere spots of dodder 

 infection, even in the districts where the^rotation system of crops prevails, 

 where pastures of mixed clovers and grasses are made to last for 4r-6 years ; 

 but the damage from dodder is nowhere very great. In Switzerland 

 the clover plant grows very luxuriantly, and this impedes the development 

 of the dodder. In the Cantons of Vaud and Geneva, and also in WaUis 

 (Valais) dodder is undoubtedly more injurious than in the other cantons ; 

 in Canton Tessin the more abundant rainfall promotes the growth of 

 the fodder, and this prevents the extension of dodder. In Tessin there 

 is no zone Which has a lower rainfall than 1,000 mm. The large-seeded 

 dodder, C. racemosa, appears only spasmodically in Switzerland, and 

 C. arvensis Beyr. is not Iniown to have appeared at all. 



In thisisohyete of 1,000 mm. we should, therefore, have a line of great 

 importance, since it denotes, in all probability, a boundary line of dodder 

 growth. 



Another boundary hne is the isohjrpse of 800 m. This boxmdary 

 line was first mentioned by Dr. J. v. Szyszylowicz, of Lemberg, on the 

 occasion of the Hamburg Conference for Seed-Testing (Jahresb. der Ver. 

 f. angeW. Bot. W. 1906 : 298). Without a doubt this also is connected 



