AbstractBranching inFontinalisoccurs primarily in the range of 5 to 15°C and differs among the species. Pool conditions reduce branching significantly among most species and can account for the reduction in growth observed in those conditions.Data on six species ofFontinalissupport the hypothesis thatFontinalisproduces more rhizoids in response to temperatures above 10°C and that this production will correspond with the summer season in the north temperate and arctic zones. Since branch production is not inhibited at 15°C and is only slightly reduced at 20°C, it appears that rhizoid production does not interfere significantly with branch production. Since rhizoid clumps often originate at branch innovations, the continuation of branching throughout the summer could aid the moss in attaching during the summer when its chances of success are maximum.