GNU Collaborative International Dictionary of English

Found one definition

1.       
   ‖Sorus , n.; pl. Sori . [NL., fr. Gr.  a heap.]
   (Bot.) One of the fruit dots, or small clusters of sporangia, on the back of the fronds of ferns.
   1913 Webster
   (a) In parasitic fungi, any mass of spores bursting through the epidermis of a host plant. (b) In lichens, a heap of soredia on the thallus.
   Webster 1913 Suppl.