“…The reaction consists either of a change of growth direction and/or velocity or in differentiation, all of which involve a functioning cytoskeleton. Such responses to environmental stimuli are gravitropism (moss protonemata, Schwuchow et al ., 1990; Walker & Sack, 1995; and references therein, algal rhizoids and protonemata, Sievers & Schnepf, 1981 and references therein, Braun & Sievers, 1994; Hodick, 1994; Leitz et al ., 1995; Braun, 1997; Hodick & Sievers, 1998: fungi, Monzer, 1996), phototropism (moss, Meske et al ., 1996: fern, Kadota & Wada, 1989, 1992: algal zygotes, Fowler & Quatrano, 1997 and references therein) and reaction to physical features, chemical gradients or electrical fields (review Sievers & Schnepf, 1981). In moss protonemata MTs are involved in the positioning of chloroplasts according to the light circumstances (review Schnepf, 1986; Abel et al ., 1989, and references therein).…”