In addition to the statocytes of roots and shoots, a number of tip-growing cells are also sensitive gravity, which affects cell growth and development. Since these tip-growing cells are highly suitable for observations in vivo, the movement and sedimentation of their statoliths can be studied in detail. Protonemata of the moss Cerato-don purpureus and Pottia intermedia were the object of the investigation of grew kinetics. The moss protonemata grown along the surface of nutrient-supplemented media in the light, and dark-grown moss protonemata were negatively gravitropic. Both gravitropic sensing and differential growth (curvature) occur in or close to the tip of the apical cell, and the tip growth is closely linked to tip orientation. The protonemata reaction on the lateral illumination depended on the quality as well as the quantity of light. The low-intensity light induced a positive phototropism of the proto­nemata, the high-intensity light produced a negative gravitropic growth.

          Besides the photo- and gravitropism of the moss protonema, the autotropism was established as an ability of protonema tip to renew the original growth direction and orientation in space after the factor inducing the tropism ceases to act. It was established experimentally that the protonema growth movements are controlled by a few stimuli at the same time, and it was suggested that disappearance even of one of them might reflect on the growth movement character. The experiments which we plan to realize during the Shuttle-97 experiment will enable us to examine the validity of this hypothesis