290 



PRACTICAL BOTANY 



and the bracken fern (Pteris aquilina), and other species of 

 Pteris, the sporangia are covered by the folded leaf margins. 

 In the walking fern (Camptosorus rhizophyllus) sori are in 



long slits arranged diag- 

 onally to the midrib. 



In the royal fern 

 (Osmunda regalis) (Fig. 

 239) sporangia are borne 

 only upon tip leaflets. 

 Such leaflets usually bear 

 dense masses of sporan- 

 gia and do little or no 

 chlorophyll work. Often, 

 however, one may see 

 a single plant exhibit- 

 ing the following grada- 

 tion in the development 

 of sporangium-bearing 

 leaflets : (1) chlorophyll 

 leaflets; (2) chlorophyll 

 leaflets with one margin 

 bearing a few sporangia ; 

 (3) one entire side of 

 a leaflet bearing sporan- 

 gia ; (4) the entire leaflet 

 bearing sporangia (Fig. 

 239, B, C, D). 



FIG. 242. A water fern (Marsilia) 



The rootstock (st), with the descending roots 

 (r) , grows in the soil at the bottom of shallow 

 pools of standing water. From the rootstock 

 the leaves (I, I', and I") arise. The expanded 

 part of the leaf may float upon the surface of 

 the water, or at times may stand ahove the 

 water. Special spore-bearing cases (s) are borne 

 upon short branches from the leafstalk 



In Clayton's fern, or 

 the " interrupted " fern 

 (^Osmunda Olaytoniana) 

 (Fig. 239), a group of 

 intermediate leaflets are entirely sporangium-bearing. In the 

 Virginia grape fern (Botrychium virginianum) (Fig. 240) 

 the leaf is differentiated into a spore-bearing branch and a 

 three-parted chlorophyll branch. In such cases the former is 

 called the sporophyll, meaning " spore leaf," and the latter the 



