CITRUS scab: its CAUSE AND CONTROL. 21 



panied by blossoms. Between these main flushes an occasional but 

 irregular putting out of vegetative parts is observed. 



In young groves which have not come into bearing the vegetative 

 growth is quite comparable with that occurring in bearing trees, the 

 chief difference being in the number of flushes. Vigorous young 

 trees which are being forced by fertilizers and cultivation are likely 

 to put on five or six distinct flushes during the first year after setting, 

 these decreasing in number until the tree begins bearing a fair crop 

 of fruit. After that time there are usually only three main flushes 

 during the year. 



Nursery trees, both budded and seedlings, are continually sending 

 out successive vegetative growths from early spring until late fall, 

 frequently making an extension of as much as 60 inches during the 

 year. Rough lemons especially have emerging leaves present prac- 

 tically throughout the entire growing season, while the sour orange 

 is inclined to be more regular in its growths, the more vigorous plants 

 putting on about 10 flushes. 



DISEASE AS INFLUENCED BY THE STOCK. 



There is a widespread popular impression that grapefruit growing 

 on rough-lemon roots is more susceptible to scab than when the same 

 variety is grown on sour-orange or grapefruit stock under the same 

 environmental conditions — that the stock lessens the resistance of 

 the scion to this disease. 



In general, scions on rough-lemon stock produce a much greater 

 vegetative growth during the first few years than is the case with other 

 popular root systems. Such being the case, trees on these roots have 

 many more leaves and perhaps a greater number of fruits passing 

 through the stages of growth susceptible to infection. Under these 

 actual conditions there is a considerable increase in the chances for 

 trees on rough-lemon roots to become infected even where resist- 

 ance remains constant. If the stock exerts an appreciable influence 

 on the inherent susceptibility to scab it should show up at least occa- 

 sionally in inoculation experiments. 



A critical study of the results from inoculation experiments 

 conducted during the past five years, coupled with the summary of 

 general orchard observations made over the same period, indicate 

 that there is no material difference in percentage or degree of in- 

 fection that could reasonably be attributed to immunizing or sen- 

 sitizing influences produced by the stock on the scion. 



ADAPTATION OF THE FUNGUS. 



That citrus scab will eventually be as serious on the round orange 

 as it now is on grapefruit is the belief of a large number of practical 

 horticulturists and a few pathologists (£3). This opinion is based 



