DISEASES OF LIME AND OTHER CITRUS TREES 205 



They consist of pink slightly hairy stalks, usually 2-5 mm, 

 in length, but sometimes longer, rather irregular in form, and 

 surmounted by a white tip or by a white opaque cluster of 

 conidia. 



The perithecia have been described as follows by South, 

 who found them on one occasion situated in groups on a rhizo- 

 morph : " The perithecia are minute, red, flask-shaped bodies, 

 the neck of the flask being often somewhat curved and about 

 as long as the diameter of the lower spherical portion of the organ. 

 Each contains asci and paraphyses. In the ascus eight, bicellular, 

 somewhat reddish-yellow transparent spores are formed, arranged 

 obliquely in a single row. The spores are bluntly pointed at 

 either end, constricted at the septum, somewhat thick-walled, 

 and measure approximately 17-20x8.5-10 microns. 



" They germinated very readily in about four hours, and in 

 culture media gave rise to rhizomorphs and Stilbum fructifica- 

 tions resembling those found on the lime trees. In cultures a 

 third form of fructification appears, of the Cephalosporium type, 

 the spores formed on the short conidiophores being very similar 

 to those borne in the head at the summit of the stalk or stroma." 



Conditions of Occurrence. 



The incidence of the disease suggests its origin from the 

 forest. In new clearings it is probably directly transferred from 

 logs or the roots of stumps : in older cultivations from infested 

 material brought down by floods. This agrees with experience 

 of the Ceylon disease, and is suspected to be the mode of origin 

 of the attack on bananas in Jamaica. Another character in 

 which the Dominica and Ceylon diseases agree is in their occur- 

 rence being restricted as a rule to swampy or sour undrained 

 soil. 



Once it is established in a lime field the spread of the disease 

 from tree to tree along the roots (it may possibly also occur 

 through the soil) is very definite and results in the death of a 

 group of trees around the original site of the infection. The 

 process of infection byjoot contact has several times been traced 

 out. 



Control. 



The preference of the fungus for undrained situations indicates 

 the point at which the attack upon this disease should be most 

 strongly pressed. A system of isolation trenches like that 

 recommended for Rosellinia disease should be established, and 

 care taken to have the trenches of good depth and linked up with 

 an effective drainage system. The disposition of dead and 

 dying trees should also follow the lines laid down for Rosellinia 

 disease. 



