Note 4 — Chapter VIII · MODIFIED CIRCUMNUTATION: MOVEMENTS EXCITED BY LIGHT.
Reading edition
In his paper, ‘Ueber orthotrope und plagiotrope Pflanzentheile’ (‘Arbeiten des Bot. Inst. in Würzburg,’ Band ii. Heft ii. 1879), Sachs has discussed the manner in which geotropism and heliotropism are affected by differences in the angles at which the organs of plants stand with respect to the direction of the incident force.