i 4 HOW TO KNOW THE FERNS 



there is no need to enter into such matters 

 at the present moment. We may, however, 

 examine a fertile leaf of the Fern in order that 

 we may start at the beginning of a really 

 interesting romance. A very small magnifica- 

 tion of the brown patches on the back of the 

 frond, which we remember are called son, 

 will reveal their true character. After removing 

 the kidney-shaped cover (indusium) we shall 

 be able to see the spore cases or sporangia 

 quite clearly. Each of these consists of a 

 capsule borne on the end of a stalk. These 

 sporangia are seen to grow out from the sides 

 of a mass of special tissue, known as the 

 placenta, from which the indusium really 

 arises. On occasions a curious club-shapecl 

 hair which secretes resin can be observed on 

 the stalks of the sporangia. There seems to 

 be no satisfactory explanation as to the part 

 which this process plays. The capsule of the 

 sporangium is much flattened, and has not 

 been inaptly compared to a watch-case. Its 

 wall is very thin, being composed of a single 

 layer of cells. Around the edges of the little 

 case there is a row of large and thickened 

 cells which form the ring or annulus. Here 

 it may be mentioned again that the structure 

 of this annulus varies greatly in the different 

 families, and is often a useful distinguishing 

 feature. To return to our Male Fern, the 

 annulus is plainly seen to start from the stalk 

 of the sporangium at one side of the capsule, 

 and it can be traced right over the top to a 

 situation about half-way down on the other 

 side. The chief business of the annulus is to 

 bring about the opening of the sporangium 

 in such a way that the spores are violently 

 expelled. This happens in the following 



