CITRUS FRUITS 127 



He also reports another root decay, due to Lyco- 

 perdon sp., which is evidenced by the usual symptoms 

 in the foliage, and which kills the trees in a very short 

 time. 



Borg reports Rhizoctonia violacea as being de- 

 structive in Malta on the roots of the citrus trees, 

 which are grown in low, clay soil. 



Polystictus liirsutus, Fries, has been reported on 

 limes in Dominica ; but it cannot be said positively 

 whether it is or is not parasitic. 



Fruit Rots. The rots of the citrus fruits are due to 

 the attacks of the various species of Penicillium (Fig. 



F;G. 54. Lemons affected with Penicillium rot. (Photo by W. T. Home.) 



54), among the most important of which are P. italicum, 

 Wehmer, P. glaucum, Link. 1 The species of this genus 

 are mostly saprophytic in nature. It has been demon- 

 strated that the fruits rarely if ever rot unless the spore 

 of the fungus gains admission through injuries in the 

 epidermis. These roots may be held in check in three 

 ways, viz. : by preventing the spores from entering the 

 fruits, by using care in picking and handling, and by 

 refrigeration and destruction of the diseased fruits. 



There is also a black rot of the orange which has 

 been reported from Arizona. It is due to Alternaria 

 citri, Pierce, which gains entrance to the fruits in the 

 same manner as the Penicillia, and must be com- 

 bated in the same way. 



1 83-11. P. d-iyitatum, (Fr.) Sacc., and P. olivaceum. 



