132 FERN. [CH. X 



mother-cells of the spores develope by cell division, and 

 finally each mother-cell divides into four spores. 



The development of the sporangium and spore is 

 here given in an abbreviated and diagrammatic manner, 

 and the formation of what is known as the ring or 

 annulus (fig. 57) has been left out. It is a line of strong 

 cells running like a crest three-quarters of the way round 

 the head of the sporangium. These cells are sensitive to 

 changes in the dampness of the air; when they are dried 

 the ring tends to uncurl and exerts a tearing force on the 

 thinner parts of the sporangium wall, which gives way 

 under the strain in the form of a gash or cleft running 

 across it. The place at which the sporangium opens will be 

 understood from fig. 57 (R) in which the cleft is not quite 

 closed. Through this gash the spores are able to escape, 

 and here their small size and lightness comes in as a 

 valuable quality, since they are borne on the wind like 

 dust, so that some at least, out of the great quantity 

 produced, hit on situations suitable for their future 

 growth. In the laboratory spores are sown on peat, or 

 better still on tiles, where they grow well and handily. 



With regard to the germination it will suffice to know 

 that the spore increases in size, and by the formation of 

 cross- walls becomes a cellular body instead of a single cell. 

 Fig. 59 b represents an early stage in the germination, or 

 in other words it represents a very young oophyte. The 

 upper part p, consisting of two cells, is green from the 

 presence of chlorophyll and carries on the work of as- 

 similation, while the lower, thinner part r.h. is colourless 

 and is a root-like organ or root-hair. Thus in the earliest 



