Fig. 18. — Concentration of hyphae of Rhabdocline pseudotsugae closely appressed 

 against the endodermal wall. The presence of protoplasmic material in the endo- 

 dermal cells was obvious, but it could not be determined whether this was a 

 manifestation of the host or of the pathogen. (X 800) 



or early May, host cells in this area rapidly broke down and the 

 hyphae multiplied in number. Thus a closely-appressed mass of 

 hyphal tissue formed, usually directly beneath the stomata (Fig. 21). 

 In mid-May, strands of hyphae toward the epidermis became 

 parallelly aligned to form a distinct hymenium. The hyphae toward 

 the interior of the needle became less appressed, large cavities devel- 

 oped and the hymenium became virtually suspended within the 

 needle. Asci and paraphyses formed at the tips of the hyphae in the 

 hymenium. Needles collected on June 4, 1956 revealed the first 

 morphologically mature ascospores. Little change, other than subse- 

 quent deterioration of the mesophyll appeared within the needles 

 throughout the remaining summer months. Two-celled ascospores 

 with germinated black cells were found in apothecia collected on 

 August 2, 1956. Whereas the hymenium was shriveled and stained 

 very heavily, a few ascospores were still visible within the asci. 



48 



