CHAPTER XXVI. 

 THE REPRODUCTION OF THE PTERIDOPHYTA. 



MATERIALS USED. 



Fertile fronds of Scolopendrium vulgare, the Hart's-tongue fern. Fresh. 

 (Alcohol material in part answers.) 



The same of the Male Fern (Aspidium Filix-mas). 



Fresh spores of Ceratopteris thalictroides, or Osmunda regalis, Gymno- 

 gramme, etc., for growing prothallia on peat, cocoanut fibre, tiles, etc. 



Prothallia of Polypodium vulgare, or other fern. Fresh. 



Fructifications of Equisetum limosum, or other species. Fresh and ripe ; 

 also unripe, fixed in alcohol, and softened in glycerine-alcohol. 



Fructifying plant of Selaginellct Martensii. Fresh, or dried. If dried mate- 

 rial, soften with potash. 



REAGENTS USED. 



Gum arable, 10 per cent. Iodine Chlorzinc iodine Potash. 



THE sporangia of Ferns stand, with few exceptions, on the 

 under side of the leaves. They usually form groups, known as 

 sori. The whole sorus is commonly covered by an outgrowth 

 of the leaf the indusium. The indusium can be very variously 

 developed. If the edge of the leaf turns over the sorus, we speak 

 of it as a false indusium. 



Sporangia of Scolopendrium. As an example for investigation 

 we select the common Hart's-tongue fern. Scolopendrium vulgare. 

 The leaf is traversed by a strong midrib, from which arise, usually 

 at right angles, weak lateral veins. The sori are formed chiefly 

 in the upper half of the fertile leaf. They have the same direction 

 as the lateral veins. Externally they appear more or less com- 

 pletely covered by two, at first overlapping, lip-like indusia, which 

 later on are more widely separated and spread open. It is only 

 necessary to prepare a delicate cross-section of a piece of a fertile 

 leaf, selecting a leaf on which the sori are already brown, but the 

 edges of the indusium have not yet spread open. We cut with 



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