remain sharp in color with their distinct borders abruptly delimiting 

 the dark green of the uninfected portions of the needle. At this 

 early stage, with the aid of a microscope, it is possible to distinguish, 

 but with some difficulty, the colorless hyphae of the parasite within 

 the needles. These hyphae are confined to the area of the lesion and 

 appear to kill the cells of the needle as they advance. Detailed 

 microscopic development is treated subsequently. 



In December or January many of the yellow flecks become brown, 

 and with further enlargement coalesce to form large necrotic spots 

 or bands. Other yellow flecks, however, remain light colored through- 

 out the winter and spring. In February or March many of the brown 

 areas are encircled by a yellow-green zone which gradually blends 

 into the healthy dark green areas. The needles in this stage of infec- 

 tion have a typical "mottled" appearance first described by Weir 

 (66) and later by von Tubeuf (61). This is a reliable symptom of the 

 Rhabdocline needle cast disease. However, von Tubeuf (61) states 

 that the mottling develops in summer and remains unchanged over 

 the winter. The author observed mottling in September of 1956 on 

 a few heavily infected trees in the Cheningo plantation. The remain- 

 der of the trees in this plantation developed mottling later, even 

 though they appeared to be as heavily infected. 



During March and April, the brown necrotic areas continue to 

 enlarge. This may be due to the killing of cells by toxic materials 

 secreted by the overwintering fungus or through desiccation of the 

 cells. Coalescence of the brown areas may become extreme causing 

 the entire needle, with the exception of the petiole, to become brown. 

 On the other hand, individual flecks may remain distinct and sepa- 

 rate, resulting later in the production of minute fruiting bodies. 

 The exclusion of the petiole from infection has been cited previously 

 by both Wilson and Wilson (70) and Brown (7) who investigated the 

 cessation of hyphal growth at the juncture of the petiole and lamina. 



The brown areas, regardless of their size, deepen in color on the 

 lower surface of the needles. Each brown area is at first slightly 

 sunken and oriented longitudinally in the direction of the bands of 

 stomates. Upon initiation and growth of the apothecia in these 

 sunken areas in April or May, the epidermis expands until it appears 

 as a cushion on the lower surface of the needle. Wilson and Wilson 

 (70) and Boyce (5) state that apothecia occasionally form on the 

 upper surface of needles, but this was not observed in the present 

 study. 



22 



