164 BOTANY. 



268. The movements of the sporangium can take place in 

 old and dried material. — If we have no fresh material to study 

 the sporangium with, we can use dried material, for the move- 

 ments of the sporangia can be well seen in dried material, pro- 

 vided it was collected at about the time the sporangia are 

 mature, that is at maturity, or soon afterward. We take some 

 of the dry sporangia (or we may wash the glycerine off those 

 which we have just studied) and mount them in water, and 

 quickly examine them with a microscope. We notice that in 

 each cell of the annulus there is a small sphere of some gas. 

 The water which bathes the walls of the annulus is absorbed by 

 some substance inside these cells. This we can see because of 

 the fact that this sphere of gas becomes smaller and smaller 

 until it is only a mere dot, when it disappears in a twinkling. 

 The water has been taken in under such pressure that it has 

 absorbed all the gas, and the farther pressure in most cases 

 closes the partly opened sporangium more completely. 



269. The annulus can snap several times.— Now we should 

 add glycerine again and draw out the water, watching the 

 sporangia at the same time. We see that the sporangia which 

 have opened and snapped once will do it again. And so they 

 may be made to go through this operation several times in suc- 

 cession. We should now note carefully the annulus, that is, 

 after the sporangia have opened by the use of glycerine. So 

 soon as they have snapped in the glycerine we can see those 

 minute spheres of gas again, and since there was no air on the 

 outside of the sporangia, but only glycerine, this gas must, it 

 is reasoned, have been given up by the water before it was all 

 drawn out of the cells. 



This movement of the annulus is a very effective provision 

 for the mechanical distribution of the spores of ferns. The 

 successive periods of wet and dry weather, or of damp or dry 

 air, when the sporangia are mature serves to open the sporan- 

 gium successively so that all the spores are scattered. This 

 opening and closing probably goes on for a considerable time 



