FILICALES 





which are only nutritive. In Dryopteris nutritive ! ind 



sporophylls are alike in outline. The young plant only produces the 

 former. But the leaves of older plants bear on their lower surfa 

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

 green or brown according to age. These are called sori t and consist 

 of sporangia with certain protective structure The sori vary greatly 



in size and form in different Ferns, which are classified according 



Fig. 387. 



Vertical section through the sorus of Dryopteris Filix-mas. (After Kny.) 



The adaxial surface is uppermost. 



to their characters. In Dryopteris, as the name implies, they are 

 kidney-shaped, as is seen in Fig. 373. Each sorus is seated on a 

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

 covering called the indusium, of kidney-like outline, beneath which are 

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

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

 and the bursting sporangia shed the spores in such numbers that t hex- 

 give a clear print of the outline of the sporophyll upon the pa] 

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

 millions. 



B.B. 2 1 



