466 SCIENCE PROGRESS 



spores and elaters under the microscope, the changes in the 

 latter can be followed readily. The elaters should be damp at 

 first and they may be taken either from fresh capsules or from 

 one which has been preserved in weak spirit. The interior of 

 the elater is filled with liquid ; as drying takes place, the mem- 

 branous parts of the wall sink inwards and the elater often 

 wriggles as it becomes more and more deformed. Then, quite 

 suddenly, it twists up and immediately straightens itself with a 

 violent spring-like movement, which commonly jerks it out of 

 the field of the microscope. If an elater which has gone through 

 these changes be examined, it will be seen to be empty of liquid 

 and apparently filled with air. But on wetting it again with 

 water or weak spirit, the liquid is very rapidly absorbed and 

 the " empty space " speedily contracts like a bubble of air under 

 rapidly increasing pressure. Apparently, however, there is no 



Fig. 4. — Elater of Liverwort (aneura) with a single spiral thickening band. 



air present, only aqueous (or spirit) vapour, for the liquid sup- 

 plied completely fills the elater in a very few seconds and no 

 bubble is seen to escape. As the liquid dries again, precisely 

 similar movements are again exhibited and they may be re- 

 peated many times. Sooner or later, however, air does leak 

 through the membrane and then the elater manifests no further 

 signs of motility or only the insignificant movements due to 

 hygroscopic changes. 



Kammerling, some years ago, showed that by cutting off the 

 extreme end of an elater the power of movement was lost. This 

 of course agrees perfectly with anticipation. Goebel, who as 

 long ago as 1895 published an admirable account of the elaters 

 in a number of genera of liverworts, remarked on the coin- 

 cidence of the movement with the moment of the disappearance 

 of their water contents and he further pointed out that in the 

 different groups of liverworts the elaters exhibited considerable 

 diversity in their behaviour. Some, e.g. in Fossombronia, are 

 scarcely motile at all, whilst in others, such as Frullania, the 

 slight independent movements the elaters are able to make 



