| Many plant organs (for example, oat coleoptiles) after reorientation into the horizontal position bend, but stop bending before reaching the vertical orientation. It is possible to write a mathematical model, where this termination is determined by plagiogravitropic component. However, the plagiogravitropism assumes the bending from vertical position toward supposed angle of plagiogrvitropic reaction. If such bending is not observed experimentally (as a rule, coleoptiles don't bend from vertical position), some alternative model might be more credible (Stočkus, 1994). |
| The apical part of the gravitropically bending organ sometimes starts to straighten before the apex reaches the vertical position (the critical angle is about 35 degrees in Coprinus cinereus). It is possible to explain this by supposing that the apical part is plagiogravitropic at this angle. However, such a model would wrongly predict the bending of the apex from the vertical position toward this supposed angle. Hence, much more complicated explanations of the phenomenon of straightening must be taken into consideration. |
| The straightening reaction, mentioned above, need not be supposed for the working model, where the attention is restricted by the apex angle. However, if we compare the whole shape of the bending organ with the experimental data, the successful model can only be written if we suppose that the gravitropic bending is complemented by some straightening reaction. The exact mechanism of this reaction is sill not clear, hence this is the area where the advantages of the more abstract imitational models can be successfully used. |
Evidently, several alternative models can sometimes be successfully fitted into one set of experimental data. However, as a rule, it is possible to choose between them using wider knowledge about the object being explored.