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In ash internodes isolated from vertical stems during winter dormancy, cambial activity was stimulated by applying an aqueous solution of auxin to the apical end and water to the basal end. The internodes maintained nearly horizontally produced cambial callus at the apical cut surface with more callus on the upper half although both halves were in contact with the same concentration of auxin. A differential response to auxin of the cambium in the upper and lower halves of the horizontally oriented internodes is postulated.
While each individual root responds to such environmental factors as light or gravity the question arises how these reactions subordinate to the whole root system, which is supposed to maintain its primary functions. Data presented here confirm that in cucumber the gravity and light modulate the growth direction of the lateral roots subunits of the system. Another important factor affecting behavior of lateral roots is an orientation of the main root. These facts all together suggest that the root system functions as an integrated entity, capable of adapting its architecture to changing environmental conditions. Its flexibility, based on unknown signaling network, guarantees optimal functioning of the system.
We tested the reactions of one species of parasitic copepod and four species of larval monogeneans to magnetic fields, and of two species of parasitic copepods and four larval monogeneans to gravity and light. All six species reacted positively to light, however, geotaxis of the two copepod species exceeded phototaxis. The larvae of Hatschekia sp. (Copepoda), Polylabroides australis and Choricotyle australiensis (Monogenea, Polyopisthocotylea) showed a significant preference for the magnetic North. Zeuxapta seriolae (Monogenea, Polyopisthocotylea) showed a magnetic South preference under enhanced magnetic intensity. Allomurraytrema spari, the only monopisthocotylean monogenean examined, did not react to magnetic fields. This suggests that the posterior appendage, which is found only in polyopisthocotylean monogeneans, may be responsible for magneto-orientation. Preference of Hatschekia, P. australis and C. australiensis for the magnetic North indicates that the magnetic field induces swimming upward. Preference for the South in Zeuxapta seriolae suggests downward swimming, thus increasing encounters with its deep swimming fish hosts. This is the first study in which magnetotaxis has been demonstrated in monogeneans and parasitic copepods.
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