General physiology; an outline of the science of life . se researchesof Strasburger comes awhole series of observationsby other investigators, whohave been able to findphototactic phenomena inall sorts of , Stahl (84) investi-gated the phototaxis ofplasmodia of Myxomycetes,previously observed by Hof-meister and Baranetzky, andfound that young plasmodiaof Acthalium septiatm are positively phototactic in half-darkness, and creep upon the surfaceof tan, but with stronger illumination they become negatively photo-tactic, and flow back again into the interior of the mass. Furthe
General physiology; an outline of the science of life . se researchesof Strasburger comes awhole series of observationsby other investigators, whohave been able to findphototactic phenomena inall sorts of , Stahl (84) investi-gated the phototaxis ofplasmodia of Myxomycetes,previously observed by Hof-meister and Baranetzky, andfound that young plasmodiaof Acthalium septiatm are positively phototactic in half-darkness, and creep upon the surfaceof tan, but with stronger illumination they become negatively photo-tactic, and flow back again into the interior of the mass. Further,Engelmann (81,3; 83) found in Bacterium chlorinum and Bacteriumphotometricum two forms that possess phototactic properties andcollect together in the light. Engelmann (82), Stahl (80), Aclerhold(88), and others 1 discovered phototactic phenomena also in theBiatomece and the Oscillarice, which behave exactly as the swarm-spores of Alga, and form very pronounced assemblages (Fig. 223).Finally, Stahl (), Klebs (85), and Aderhold () demonstrated. Fig. 223.—Phototaxis of Diatomece. A particle of mudwhich was thickly surrounded by Diatomeie liesin the middle of the drop. The organisms haveall crept toward the edge turned toward the sun. 1 Cf. Verworn (89, 1). G G 450 GENERAL PHYSIOLOGY phototactic movements in the Dcsmidiacece, and showed that thesealga-cells place themselves with their long axis parallel to thelight-rays, and in this position, by the extrusion of their secretion,move along the bottom in their peculiar manner toward thesource of light, or with greater intensity away from the source(Fig. 224). In a preparation containing living Closteria x or Pleuro-tamice all individuals place themselves with their long axis parallelto one another and to the direction of the incident , we find that among unicellular organisms, so far as they areirritable at all to light, phototaxis is a wide-spread phenomenon. After phototactic phenomena had been discovered
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