Pomona College Journal of Economic Botany 



35 



Mr. Hume gives the following about the disease on the fruit of the pomelo : 

 "Upon the fruit the disease is first manifested by the irregular brownish dis- 

 coloration. This discolored area is irregularly defined around the margin. 

 The diseased spot may be on any portion of the fruit and may vary from 

 an inch or so in diameter to an area nearly equal to that of the outside 

 of the fruit. As it progresses these spots gradually change in color, some- 

 times becoming grayish, sometimes somewhat lighter. Ultimately, however, 

 the whole affected area becomes dirty black in color. If the point of in- 

 fection is small at first it gradually enlarges under favorable conditions so 

 as to embrace the whole fruit. Sometimes the affected area remains constant 

 in size for a considerable time, in which case in its older stage it varies from 

 black at the center through various shades of brown, brownish yellow to the 

 normal yellowish color of the healthy rind at the margin." Fla. Agrcl. Exp. 

 Sta. Bull. No. 74, pp. 165-166, Aug., 1904. 



Figure 19. 



Details of fruiting bodies of wither-tip fungus: A, acervulus with compact con- 

 tents of setae, conidiophores and eonidia (original); B, acervulus in more advanced 

 stage, the spores escaping (original); 0, conidiophores, eonidia and setae (after Hume); 

 D, enlarged portion of B; E, cross section of acervulus after McCullough in Bull. 52, 

 U. S. Dept. Agrcl. 



SPECIFIC DESCRIPTION 

 This fungus is strictly parasitic, e. g., . feeds directly upon the tissues 

 of the host plant. The eonidia (spores) are very minute regularly oval 

 bodies which are admitted into the tissues of the host by means of small 

 punctures or abrasions of any kind. Here they germinate, forming rather 

 stout mycelium, which penetrates the plant cells, and through which the 

 fungus draws all food. Not until the tissues of the plant are killed are 

 the acervuli (fruiting bodies) produced. These acervuli contain the eonidia 

 or spores which develop within the little sac. As soon as they are produced 

 from the mycelium they shove themselves through the surface of the host 

 and when the eonidia are ripe the top opens up allowing them to escape. 



