A p h m izomei~on flos-trqutce : some FGx)lopical Implicatioiis r . l h e I'liiitosyiitlirtic ch;tractc.rist irs of diffewnt nutiiral p i~i i i l i i t ions of ~l~~h t r n i . -; o~/ i r .~~~o~~ ///ist r p r t r s RALFS ex 130~s. et YLAII. wrre mwsiirctd in laboratory. Two types of A . flos-nqrtn~. p;irtl>rar. kZebrlh.nii (sniall needle-like colonies, 0.1-11.3 nim long on tlie ;iverage. growing at t i x n s p i rrnry r e d u c d by high density of nanoplmkton to about 0.5 in) and partly n r . flos-tryutre (colonies flake-like up t,o 20 inm long. which grow when transp;ciwicy in nhout 1.6 m or Jiiplicr) \i'rre investigated. The photos?..nthesis-irI.ndinnrc. (P-1) curvt~s of var. klrhnhnii were ehiirnctciizctl hy ii high value of the initial slope arid pliutoiiihihit inn ;it rel;Ltively Ioa. light intensitirs (2.50-400 pK . m-2 * 8-1). In var. f[os-cqrure the P-Z ciirvc:s 1i;icl a lower init iiil slope ;ind n c i plic'toiiiliibitioii wzns ohserved in tlie ixiige of irradiance to 450 pE . Inz . s-I. The effect of diffrreiit s i 7 . r~ of colonies on pliotnnpnt.he.sis ;md pusfliibk inipirc.1 of strong light (induced by U n p h i t r feeding ustivity) t o promoting the large-flakes .4phnnisonccrro?r iii tlir prrscncc' of I;irge Utrph.7tiir are tl i sell sncd. 111 the past few years two different t y p of thc wnliiier water I)looai of Ap/tio1;:f+ 7tlCIMJ71 flwuyune RALFS ex BORN. et FLAII. qqwarcd in fish ponds Nitrintcd west wtirtln front the town of Hlatnh (Southorn Boheniia, Czechoslovakiu). Tlicsc tylJeS wcrtb iheraiined partly as VBr. fh-aquftc and partly R s vRr. k/rlni/i#ii EI.EIK. The typical var. //os-urpiar, whivh foriiied flake-like (or grass hladib) coloniesi up t o 20 nini long, was regiiliirly reported froiii thrsc fish ponds ( H R B~~E B 1905, h'oki~lsn 1907, lh)*m el (11. 1954, Fom c.t id. 1980). Var. kZrbdi)t.ii, with stitnll, on t l i e average 0.1 -0.8 HIIII long needle-like colonicrs appeared niore frcyucntly i n plankton in the laat yews. llorphoiiict rice vharacteristics of thew viii ic*t ivs (cell dinirnsions) corresponticci to dnt:i of Y . I E R~I N~S T A~ (1966) ant1 KONDRATEVA (1972) for Al~~lcinizonterlit11 flos-aquae (identical with A. /io.w~qwic var. /~~M -~I~u c c c )nncl A. flrvr-nc/lriie w r . kIt&i/t#ii EIAXIZ. Both types wcre always distinguishable. Their occurrence toget her in the mnic I;md was rare and i n them C A S~R neither types of A~~/irr)/.~:oF~te/ro,i fornietl 11 niorc xtit)stiiiitiid part of phytoplankton. l)ennc water hhmiii t v a~ always thc conNcqiienc~c* of the nias8 clevelopnient of only on(. of 1 hcnr varieties.Great variiition i n colony k z e , evcn II tcndeticy to lose the coloniiil hnhit, h n w twcw reported in the literature (cf. MC~ACHLAX rt cd. 1963, BAKER 1981). According t o McLacrii,.w el rtl. (1963) the colony shnpc anti size appcw to he rcgulntcvl piirtly by hcrctlit~ tin(\ partly by nutrition. IAr.,ucit (1980) sugprxted tlint Dcrphtrirr ((mitinonly