on 0.02% malt extract agar displayed spiralling of the colony in a clockwise direction (viewed from above the agar plate). Only hyphae at the agar surface contributed to this spiral aspect. The direction of curvature of individual hyphae was related to their supporting surface; hyphae curved to the right as they advanced over the surface. This sustained departure from straight growth is attributed to a displacement of the plastic apex of the hypha to the right as a result of its own clockwise axial rotation (as viewed tipwards from within the hypha). Attempts to observe directly the rotation of the apex failed. Calculations show that the rate of angular rotation of an individual leading hypha was of the order of 500° per millimetre of extension, a rate similar to that in several other cells which spiral as they grow. However the angle of spiral growth was very small (about 0.7°). Out of 157 isolates of fungi tested, 21 showed pronounced spiralling of their colonies on 0.02% malt extract agar and 39 showed weak spiralling, whence it is inferred that spiral growth of individual vegetative hyphae is of widespread occurrence amongst fungi.


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