IIQ6 DISKASKS not DUK to r.VRASITKS OR or TTXKXOWX OBKUX 



late types which might be capable ol' displacing the phase of maxiniuni re- 

 ceptivity, that is to say, the moment when growth is most rapid and most 

 intense, to a point far ahead in the season, so as to make this phase coincide 

 with a more favourable weather period. The Marsh seedless variety would 

 be well adapted for this pur|)o?e. The qualit}' of the host on which C. de- 

 iiimana var. Pomelo has been grafted also influences the development of the 

 disease. The disease is more frequent in plants grafted on the wild lemon 

 tree than in those grafted on the bitter orange (C. Aurantium var. amara) ^ 

 which are not so earl3^ 



The injury caused every year by this disease to the crop of C. decumana 

 var. Pomelo in Florida totals ,$ 50.000, and still greater injury is reported 

 at Cuba, Porto-Rico and the Pine islands. 



It is obvious from the foregoing that humidity is one of the most im- 

 portant factors in the development of the disease. When the small leaves 

 begin to open, during the phase of rapid growth of the leaf, numerous small 

 drops of dew form on both surfaces o^^ theleaf during the night, the quantity 

 varying according to the relative humidity of the air. If the latter remains 

 neai the dew point, the droplets combine to form one continuous layer of 

 water, which covers the underside of the leaf for several days at a time. If 

 on the other hand the air becomes very, dry, the water which has accum- 

 ulated during the night evaporates during the earh' hours of the da}'. 



The moisture of the air and the presence of a water film on the leaves 

 form very favourable conditions for the development of the disease. What 

 is the deduction to be made from these circumstances with respect to the 

 origin of the disease ? 



It is a well known fact that the acidity of citrus fruits becomes more 

 pronounced in proportion as the humidity of the atmosphere increases and 

 the temperature is lowered. Therefore the question at once suggests itself 

 whether there is not a relation of cause and effect between the development 

 of the disease and excessive aciditv due to the wet and cold weather. 



Localities 



Materials used 



of 



trees 



Counted 



Total Healthy fruits 

 Numljer 

 of 1 

 fruits Number 



Scabbv fruits 



1 Number 



Orlando Bordeaux mixture. . . 5 



No trLatment I 4 



I,ime-Sulplmr g 



Bradentown i Eordeaux mixture. . . 2 



No treatment 4 



lyime-Sulphur I 4 



Soluble sulphur (poly- 

 sulphide of sodium) . I 4 



1281 

 1262 



2371 

 628 



597 

 1024 



843 



6 



542 



587 



88 



527 

 454 



30-/3 



99 V2 



77 Vs 



6V2 



85 V2 



48 'U 



46 V2 



