310 PRACTICAL BOTANY 



peculiarly thickened walls, which constitute the ring, 

 or annulus, and thinner-walled, flattened cells, which 

 together form the lateral walls of the completely 

 closed sporangium. 



Place a number of mature, but not yet ruptured 

 sporangia upon a dry slide : warm them very gently over 

 a spirit-lamp, and observe quickly under a low power : 

 note the sudden explosive rupture of the sporangia, so 

 as to eject and scatter the spores : this is due to the 

 straightening of the annulus or ring. Similar results 

 may be obtained by mounting in water, and subsequently 

 adding glycerine ; in fact, on the removal of water by 

 evaporation into the air, or by a reagent such as glycerine, 

 the curved annulus tends to straighten itself, and then 

 ruptures the thin wall of the sporangium. 



Note sporangia in which the thin lateral walls have 

 been ruptured transversely, the ring having straightened 

 itself out : now breathe on the sporangia, and note that 

 on being thus moistened by the breath the annulus 

 becomes more curved, while on being left exposed to 

 the dry air for a few minutes it again becomes 

 straight. 



Examine single spores under a high power : they are 

 unicellular bodies, having a brown wall, with external 

 band-like outgrowths of the exospore or outer layer 

 of the wall. All the spores are alike (Homosporous). 



The various stages of development of the sporangium may be 

 found in any sorus in which only the first sporangia have come 

 to maturity : treat the sections previously with weak potash ; if 

 this makes them too transparent, neutralize with weak acetic acid, 

 and mount in glycerine ; or the sections may be treated at once 

 with " eau de javelle, " and then be mounted in glycerine. 



