252 



MORPHOLOG Y. 



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

 pinna; here. 



531. Fruit ''dots" (soriis, indusium). — If we examine the 

 under side of such short pinna; of the Christmas fern we see that 

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

 , the pinna. These are called the " t'ruit 

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

 we examine it with a low iiower of the mi- 

 croscope, 

 or with a 

 p o c k e t 

 lens, we 

 see that 

 there is a 

 c i r c u 1 ar 

 disk which 

 c o vers 

 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 indu- 

 sium, and it is a sjiecial 

 outgrowth of the epidermis 

 of the leaf here lor 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 spoi\vii;ia^ This 

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

 others, is attached to the leaf b\- means of a short slender stalk 



Kig. JSO. 

 Christmas fern (Aspidium acrostichuides). 



