NEPHRODIUM SPOROPHYTE 173 



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 gly- 

 cerine, 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. 



B.THE GAMETOPHYTE, OR OOPHYTE. 



I. Dry some of the leaves of the Male Fern, which bear sori, 

 on a piece of paper : the spores will then be set free by the 

 rupture of the sporangia, and they may thus be collected in 

 large quantities. Sow some of them on damp earth : keep 



