2S8 



THE ASCOMYCETES 



eri on /. virginiana. The asci of K. tetraspora contain 4 asco- 

 spores; those of K. juniper i, 8. Keithia tsiigae on Tsiiga canaden- 

 sis also has asci with 4 spores. The asci of K. thujina on Tbiija 

 occidentalis and K. chamaecyparissi on Chavmecyparis thyoides, 

 however, contain 2 spores. The black apothecia usually occur 



Fig. 104. Rhytimia acerininn, causing tar-spot on maple. A. Apothecial 

 sorus with a variously contoured surface that ruptures irregularly. B. 

 Melasmia or conidial stage in vertical section. C. Conidiophore and conidia 

 enlarged. This stage may be spermatiophore and spermatia, instead. D. 

 Archicarp with three "trichogyne" cells borne on slender stalk. The asco- 

 gonium cell is basal, septa are perforate, and nuclei are migrating into 

 ascogonium cell. E. Ascogenous hypha arising from ascogonium, nuclei 

 paired; penultimate cell has two pairs of nuclei and may again hook and 

 branch. F. Vertical section of apothecial stroma in diagram. A mucilagi- 

 nous cavity at apex aids in rupture and the freeing of ascospores. G. Single 



ascus enlarged. (Adapted from Jones.) 



