PERNS 



3 6 9 



fern roots spread through the decaying mass of leaves obtaining 

 also some food. Another kind of dimorphism is present in 

 several of our common ferns. Here, as in the 

 sensitive fern (Onoclea sensibilis], there are 

 certain leaves with large, expanded green 

 blades. These perform the function of photo- 

 synthesis. Other leaves have stalks (or 

 petioles) equally long, but the blade of the leaf 

 is very much contracted and the leaflets inrolled. 

 These are the fertile leaves, and bear the spore 

 cases in crowded sori within the roll of the 

 leaflets. The vegetative leaves arise early in 

 the season, while the spore-bearing leaves 

 (sporophylls) are developed later, some time in 

 June. If one cuts off the vegetative leaves in 

 the spring, as soon as they attain a height of 

 Young plant of Pteris 20-30 cm. (8-12 inches), the very young spore- 



serrulata still attached , 



to prothaiiium. bearing leaves will change to vegetative ones, 



Fig. 336. 

 Staghorn fern (Platyccrium alcicorne). 



and many of them will be intermediate between the hvo. If the 

 experiment is to be performed, it is well to cut the vegetative 

 24 



