Wed. morning G. mentioned dimorphic forms of rap. of bry. at Roscoff - you can see 2 forms have different colours in field but under microscope there is no apparent morph. difference G. noted that hybridization is imp. in bry. but we virtually know nothing about the phenomenon Thurs. Field Trip to St. Pol. Bry. occur most abundantly where there is rock & sand - this provides sufficient "in-fauna" for food, under ledges covered by algae. Ctenostomes in upper intertidal area on algae.