1 8 OUR NATIVE FERNS AND THEIR ALLIES. 



large, imbricated, scalelike indusia which are fixed by their 



bases to short, oblique veinlets. 



56. Ornithopteris. — In this the two lowest branches of 



the frond bear panicles of fruit at tlie end of very long stalks. 

 The ovate sporangia are sessile in two rows along 

 the branchlets of the panicle, without special 

 covering of any kind. In the section represented 

 by our species the veins are free. 



57. SchizEea. — In this genus the large ovoid 

 sporangia are sessile in double rows along the 

 single vein of the narrow fertile divisions. In 

 our species the pairs of fertile pinnae form a dis- 

 tichous spike (Fig. ii). 



58. Osmunda has the large globose spo- 

 rangia, short-stalked, and borne on the con- 

 tracted fertile portions of the frond. In the cin- 

 namon-fern (0. cinnamomea) the fertile fronds 

 are entirely distinct from the sterile, yet mani- 

 festing a tendency to variation in the var. fron^ 

 dosa. In the interrupted flowering-fern (0. 

 Claytoniana) the fructification is confined to a 

 few of the middle pinnae of the frond. In the 

 royal flowering-fern (O. regalis) the fructifica- 

 tion is borne at the apex of the fronds. 



59. Spores. — The spores of ferns constitute 

 the so-called fruit. A spore consists of two* disr 

 tinct closed sacs and the cell contents, all of 

 which differ from each other not only in struc- 

 ture, but also in chemical composition. The 



Fig II —SchiziBa o"*^'' layer (exospore) consists chiefly of cellu- 

 Pursh. lose ; the inner layer {endospore) contains some 

 albuminous matter in addition, while the cell 

 contents consist chiefly of a thin, colorless, jelly-like substance 

 known as protoplasm, with grains of chlorophyll (the green 



pusilla 

 Entire plant, 

 ural size. 



* Campbell has recently demonstrated the existence of a third (middle) 

 layer, which is not readily apparent until after germination. Cf. Memoirs 

 Boston Soc. Nat. History, IV, 17 et seg. (April, 1887). 



