Capillitium of Trichia
In Trichia and Hemitrichia the capillitial threads have spiral thickenings. This gives the capillitium a rope-like appearance under the microscope. The threads take up and lose water vapour and this causes changes in the tensions along the thread. Relieving these tensions results in a wriggling action of the thread.
To Observe this Phenomenon
If you examine a sporangium of a Hemitrichia under a dissecting microscope, the heat from the bulb will activate this system and result in quite violent movements of the threads. These movements of the capillitium are sufficient to expel the spores from the sporangium. In this way the spores can be released slowly over an extended period of time and that is obviously a good strategy.
Students: Why 'obviously'?