FILICALES 



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and chiefly in the apical region, numerous groups of organs which are 

 green or brown according to age. These arc called sori, and consist 

 of sporangia with certain protective structures The sori vary 

 greatly in size and form in different Ferns, which arc classified accord- 

 ing to their characters. In Nephrodium^ as the name implies, they 

 are kidney-shaped, as is seen in Fig. 266. Each sorus is seated on a 

 vein, which provides its necessary nourisimient. It is protected by a 



^ 



Vertical section through the sorus of Nephrodium Filix-nuis. (After Kiiy.) 

 The adaxial surface is uppermost. 



covering called the indusium, of kidneydike outHne, beneath which are 

 numerous sporangia. If a leaf bearing mature sori be laid on a sheet 

 nf paper to dry, with its lower surface downwards, the indusia shrivel, 

 ind the bursting sporangia shed the spores in such numbers that they 

 give a clear print of the outline of the sporophyll upon the paper. 

 The spores are dark-coloured, very minute, and are produced in 

 millions. 



A vertical section through the sorus of Nephrodium shows an 

 ' nlarged receptacle, traversed by the vascular strand. The indusium 

 rising from it overarches the numerous sporangia which arc attached 

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