686 EXPERIMENT STATION RECORD. 



determine wliether diseaseil plants became centers for the further spread of the 

 disease sliowed tliat they did not. 



An effort was made to determine whether weather conditions were influential in 

 connection with the occurrence of the disease. Tlie results were not conclusive, but 

 it is pointed out that more diseased plants were found after a heavy rainfall and a 

 day of hijj:h temperature than at other times. 



While the author reco<^nizes the fact that the disease can be caused by the injec- 

 tion of sap from diseased plants into healthy ones, he denies that the disease can be 

 communicated by the external application of the diseased sap, provided care is taken 

 that the diseased sap does not run down the stena and get into the soil among the 

 roots. 



To determine whether the seed used influenced the presence of the disease, seeds 

 were selectt^d from healthy and from diseased plants, but no marked difference was 

 observed in the results. In a test with small, large, and medium-sized seeds it was 

 found that the medium-sized seeds produced the smallest percentages of diseased 

 plants, while the number of diseased plants from the large and small seeds was about 

 equal. 



In regard to the cause of this disease the author, while admitting that it is physi- 

 ological, contends that it is not due to the retarding effect of oxydase and peroxydase 

 on diastatic ferments. He has previously maintained that the apparent excess of 

 oxidizing enzyms in the diseased leaf was really due to the smaller amount of sugar, 

 tannin, and organic acids contained in these leaves, as compared with that contained 

 in healthy leaves, and in the present paper he states that these enzyms do not retard 

 the conversion of starch into sugar. Ten cc. of a solution giving a strong reaction 

 with guaiac were added to 25 cc. of potato starch in 1 per cent solution, and 20 mg. 

 pure diastase and an equal amount of the same oxydase solution, after being heated 

 at 110° for half an hour, was added to a like amount of starch and diastase. The 

 heated solution gave no reaction with guaiac. The conversion of the starch into 

 sugar proceeded with the same rapidity in both cases, the active oxydase in the one 

 solution having no retarding effect. 



Believing that the retarding effect observed by some authors was due to the pres- 

 ence of tannic acid, the author prepared a solution of this acid from the alcoholic 

 extract of tobacco leaves and added this to the oxydase solution. In one case this 

 was heated so as to precipitate the tannic acid and thus render it inactive. The 

 results showed that in the solution containing the unheated tannic acid the conver- 

 sion of the starch proceeded much more slowly than in the other solution, thus con- 

 firming his opinion. He also maintains that oxidizing enzyms will not diffuse and 

 hence can not be taken up by the roots of plants. 



The author is unable to throw light on the nature of the disease. In general he 

 attributes it to the inability, of the thin-leaved Deli tobacco to withstand unfavorable 

 external influences, or, in other words, to the constitutional weakness of a close-bred 

 strain, by reason of which the physiological processes are distur]:)ed l)y unfavorable 

 surroundings. He admits, however, that he is unable to exjilain the phenomenon of 

 infection, and that his exjilanation of the disease is incomplete. The remedy sug- 

 gested is to breed resistant ])lants.— h. m. pieters. 



Fungus diseases of cotton, L. Lewton-Brain ( West Indian BuL, 4 {1903), No. 

 3, pp. 255-267, figs. 3). — Descriptions are given of anumber of fungus diseases of cotton, 

 the information being largely drawn from publications of this Department, the 

 Alabama Station, etc. 



A fruiting stage of Rhizoctonia solani, F. M. Rolfs {Science, n. ser., 18 {1903), 

 No. 466, p. 729). — While studying the Rhizoctonia of the potato, the author became 

 convinced that the fungus is not a sterile one, as has been frequently claimed, and 

 much time has been given to a study of the fruiting stage. 



