146 



FUNGOUS DISEASES OF PLANTS 



PYTHIACYSTIS.^( After 



fungus penetrates the rind and other fibrous portions of the 

 lemon to a considerable extent ; it is much branched, irregular 

 in diameter, and extensive. Upon the lemon, as a rule, no form 

 of spore is produced, but there is developed frequently a con- 

 spicuous aerial growth due to the emergence 

 of many mycelial branches. In some cases 

 these are produced in more or less tuber- 

 culate masses. Conidia and sporangia appear 

 under favorable conditions. In moist soil near 

 affected fruit the sporangia are developed 

 abundantly upon a fine much-branched my- 

 celium (Fig. 47). The sporangia measure 

 2060x3090^ (averaging 35 x 50 /x). 

 They are lemon-shaped, or subspherical with 

 pronounced apical protuberance. In water 

 FIG. 47. SPORANGIA OF germination is effected by means of a vari- 

 aUe number Qf zoosporeSj often about thirtVj 



each biciliate with long cilia (Fig. 48). 

 Control. Ordinarily the fungus does not produce any spore 

 stage upon the surface of the lemon. On moist soil, however, 

 it produces sporangia and sometimes conidia. 

 The infection of the fruit usually takes place v C Q 

 in the orchards, and also subsequently by "^W 

 direct contact and also by the operation of 

 washing. It has been found, for instance, 

 that if uninfected lemons are dipped in water 

 in which diseased ones have been washed, 

 infection will in time result on the healthy 

 fruit. In fact, the ordinary wash water may 

 itself contain a large number of germs of 

 this fungus and it may also live more or less FlG . 48 . GERMINATING 

 permanently in the machine used for wash- SPORANGIUM OF PYTHIA- 

 ing such fruit. The remedy, therefore, for CYSTIS. (After R.E. Smith) 

 such conditions is very simple and merely consists in treating 

 the water used for washing purposes with some aseptic or toxic 

 agent. The most practicable method which has been devised con- 

 sists in using copper sulfate, formalin, or potassium permanganate. 

 In using formalin one part of the reagent to ten thousand parts 



