792 



SCIENCE 



[N. S. Vol. XXXI. No. 803 



uary 19 and March 12, 1908, began to produce 

 fresh uredospores within six days after trans- 

 planting. In the field fresh rust pustules on 

 new growth of timothy were common from March 

 13 on. Thus the rust mycelium is able to live 

 through the winter in this locality. How the 

 rust winters further north has not been deter- 

 mined. The teleuto stage is more common in 

 Pennsylvania and New York than at the Arlington 

 Experiment Farm, but as the secial stage is per- 

 haps rare in the United States the occurrence of 

 teleutospores is of doubtful importance. 



In timothy-breeding work at the Arlington 

 Experiment Farm in 1908 and 1909, W. J. Morse, 

 of the United States Department of Agriculture, 

 found that the difference in varietal resistance of 

 timothies to rust is well marked. This has also 

 been determined in greenhouse experiments, and, 

 although no variety or strain of timothy has 

 been found to be entirely immune, there is a very 

 noticeable dilference in the degree of suscepti- 

 bility of the different varieties to rust. 

 Floret Sterility of Wheats in the Southwest: 

 Mr. Edw. C. Johnson, Bureau of Plant In- 

 dustry. 



Floret sterility of wheat, or the non-develop- 

 ment of kernels in florets of otherwise normal 

 spikelets, is common in the southwest, especially 

 in parts of Texas and Oklahoma. The trouble has 

 been variously attributed to insects, imperfect 

 fungi, rusts and physiological conditions, but until 

 recently no experiments have been performed to 

 demonstrate what are the principal causes. 



In 1908 and 1909 investigations were under- 

 taken at San Antonio, Texas. There the per cent, 

 of sterile florets in wheats was 30 to 50 per cent, 

 and 12 to 15 per cent, for the two years, respect- 

 ively. Although the exact role played by wheat 

 thrips was not established, their importance as 

 agents for spore dissemination was noticed. As 

 many as five rust spores and three conidial spores 

 of imperfect fungi were observed on the antennas 

 and appendages of a single thrip. As the thrips 

 are exceedingly active and penetrate between the 

 glumes of florets, spores are often carried into the 

 young wheat flowers. 



Ovaries of sterile florets were almost invariably 

 afi'ected with fungi. Cladosporimn graminum 

 Cda., and Stemphylium n. sp. were common on 

 the leaves and diseased ovaries of affected grain 

 and rusts, both Puceinia- graminis Pers. and 

 Pucoima rubigo-vera (D. C.) Wint., almost in- 

 variably were present in the florets. Inoculation 

 of florets with spores of pure cultures of Clado- 



sporium graminum Cda. and Stemphylium n. sp. 

 were made by dropping a mixture of spores and 

 water between the glumes held apart with 

 tweezers. This increased the percentage of sterile 

 florets. The increase amounted to three per cent, 

 where 432 florets were inoculated with the former 

 species and 195 florets similarly treated with 

 sterile water were used for control, and 1.9 and 

 9.19 per cent., respectively, where 186 and 301 

 florets were inoculated with the latter, and 195 

 and 198 florets treated with sterile water were 

 used for controls. 



Similar inoculations with uredospores of Puc- 

 einia graminis increased the sterility 21.03 per 

 cent, where 93 florets were inoculated and 206 

 florets were used for control. In two sets of 

 inoculations where the wheat heads were soaked 

 in water full of spores an increase of sterility of 

 7.36 per cent, and 6.08 per cent, resulted where 

 85 florets and 264 florets, respectively, were in- 

 oculated and 106 florets and 151 florets similarly 

 treated with sterile water were used for controls. 



No precautions were taken to prevent drying 

 of the heads after inoculation, except covering 

 both inoculated and control heads with tissue 

 paper for two days. In the hot, clear days which 

 followed the heads dried very quickly and the 

 per cent, of infection was reduced. In an experi- 

 ment where the wheat plants were screened from 

 the direct rays of the sun an increase of sterility 

 of 12.32 per cent, above that in adjacent unshaded 

 control plants resulted. No artificial inoculation 

 was performed. Shading prevented rapid drying 

 in the mornings and thus gave better conditions 

 for the development of fungi. 



The experiments show that rusts and associated 

 fungi, chief of which is Stemphylium n. sp., are 

 undoubtedly the most important causes of floret 

 sterility of wheats in the southwest. That similar 

 conditions often exist in other localities was dem- 

 onstrated at Minnesota in 1909. In the plats for 

 rust resistance breeding all the grains when in 

 bloom were sprayed with rust spores. In all the 

 non-resistant wheats a large per cent, of the 

 florets produced no kernels on account of rust 

 infection in the heads, while in adjacent un- 

 sprayed plats such sterility was not marked. 



Bacterial Blight of Mulberry: Dr. Ebwin F. 



Smith, Department of Agriculture. 



In 1890 Cuboni and Garbini studied a disease 

 of the mulberry about Verona. This was ascribed 

 to a Diplocoecus believed to be identical with or 

 akin to Streptococcus hombycis, supposed to be 

 the cause of a disease of silk-worms. Successful 



