252 



MORPHOLOG }'. 



middle portion toward the end. This is because of the shorter 

 pinnae here. 



531. Fruit "dots" (sorus, indusium). If we examine the 

 under side of such short pinnae of the Christmas fern \ve see that 

 there are two rows of small circular dots, one row on either side of 

 ( the pinna. These are called the "fruit 

 dots," or sori (a single one is a sorus). If 

 we examine it with a low power of the mi- 

 croscope, 

 or with a 

 p o c k e t 

 lens, we 

 see that 

 there is a 

 circular 

 disk which 

 c o v e r s 

 more or 

 less com- 

 pletelyvery 

 minute objects, usual- 

 ly the ends of the 

 latter projecting just be- 

 yond the edge if they are 

 mature. This circular disk 

 is what is called the indti- 

 sium, and it is a special 

 outgrowth of the epidermis 

 of the leaf here for the 

 protection of the spore- 

 cases. These minute ob- 

 jects underneath are the 

 fruit bodies, which in the 

 case of the ferns and their allies are called sporangia. This 

 indusium in the case of the Christmas fern, and also in some 

 Others, is attached to the leaf by means of a short slender stalk 



Fig. 286. 

 Christmas fern (Aspidium acrostichoides). 



