14 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



vines sprayed with the acid iron sulfate were greener than the wit- 

 nesses, at least during the first part of the growing season ; the vines 

 sprayed with the Bordeaux mixture were much greener than the wit- 

 nesses, even in the height of summer. This improvement in the color 

 of the foliage, where and whenever the above fungicides are used, occurs 

 regardless of the presence or absence of disease. 



The Red-leaf disease first appeared in the plot on the 10th of June, 

 when a single vine was found somewhat affected. On the 10th of July 

 there was hardly more than one per cent of the vines affected. From 

 then to the end of the season, however, the disease rapidly increased. 

 On the 25th of August about ten per cent of the vines were affected, 

 which gives an increase of nine per cent in thirty-six days. From the 

 25th of August to the 13th of October-, the increase was only five per 

 cent. 



If, instead of considering the plots as a whole, we compare the percentages of 

 diseased vines among the sprayed and unsprayed rows, we will find that the Red-leaf 

 disease develops almost as freely in the one case as in the other, with one exception. 

 In the case of the witnesses (average of seven sections) the disease is more rapid from 

 the 10th to the 28th of July than in the case of the sprayed vines ; but between July 28th 

 and August 25th it is proportionately less rapid than among the vines sprayed with the 

 acid iron sulfate and not much greater than among those sprayed with the Bordeaux 

 mixture. The rapid rise in the percentage of diseased vines in the sprayed rows begins 

 later than in the average of the witnesses, and on the 28th of July. On the 12th of 

 August the vines sprayed with the iron sulfate show a greater percentage of diseased 

 vines than the witnesses, and throughout the remainder of the season continue to do so. 

 Among the vines sprayed with the Bordeaux mixture the percentage of disease remains 

 below that of the witnesses, except on the 13th of October, when it is almost one percent 

 higher. The vines sprayed with the iron sulfate and Bordeaux mixture (one section) 

 showed 1.6 per cent diseased vines all through July; between July 28th and August 12th 

 the percentage increased to 5.4 per cent, and from that date until October 13th the 

 number of diseased vines gradually increased until it reached 9.3 per cent. (See Fig. 2.) 



The distribution of the diseased vines in the plot is quite sporadic. 

 The disease does not progress from any one center, or many centers. 



In the map (Fig. 1) the position of the diseased vines on October 13th 

 is marked by a circle; the crosses representing the vines. The reader 

 will at once notice that the diseased vines are very scattered, their 

 grouping very indefinite, and he would be unable to tell from the map 

 where the disease first started. On the 10th of June there was one 

 diseased vine in sections 6, 8, 12. On the map, which shows the posi- 

 tion of the diseased vines on October 13th, there is not the remotest 

 suggestion of four centers of infection. From this fact we may conclude 

 that priority of infection has little to do with the spread of the Red-leaf 

 disease. And this is the more especially worthy of note since priority 

 of infection is generally a most decided factor in the spread of parasitic 

 diseases. The reader has only to recall to mind the action of the 

 Phylloxera, the Root-rot, the Mildew, etc. The parasite causing a given 

 disease may spread from one plant to another in a more or less regular 



