608 



Thirty-second Annual Report 



the attack of Aspergillus, Penicillium and other more or less 

 saprophytic organisms. Sterigmatocystis has appeared in a 

 very few cultures. Inoculations which will determine the na- 

 ture of the bacterium are under way. 



Histological studies explain the symptoms observed in con- 

 nection with the date-rot disease. Cells at and near the surface 

 of an attacked spot develop a brown pigment. In the meantime, 

 the parasitic hyphae advance through and between the cells, 

 branching freely and becoming swollen where they lie in the 

 protoplasmic contents of the cells which they soon destroy. 

 The advance toward the center of the fruit is checked for a 

 time when the tannin layer of the date fruit is reached, but the 

 hyphae now spread more rapidly parallel with the surface of 

 the fruit, entirely destroying the parenchymatous tissue and 

 leaving a cavity under the cuticle and epiderm which fills with 

 air and results in the blistered appearance. By the time the 

 tannin layer is penetrated the blister is usually very large. As 

 previously stated, several infected spots may coalesce to form 

 one large spot. Lateral growth of the hyphae just beneath the 

 surface in some cases is rapid, resulting in an extensive brown- 

 ing of the fruit before blisters appear. After a blister has 





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Pig. 7. — Field of lettuce near Toltec. infected with bacterial rot. 



