158 



PLANT STEUCTUEES 



tvijcltium) (Fig. 129) and adder's tongue (OpJiioglossum) 

 (Fig. 130). It is important to note, however, that the 

 Horsetails and Club-mosses are Eusporangiates, as well as 

 all the Seed-plants. 



Another small but interesting group of Ferns includes 

 the "Water-ferns,"' floating forms or sometimes on muddy- 

 flats. The common Miirsilia may be taken as a type (Fig. 



133). The slender creeping stem 

 sends down numerous roots into 

 the mucky soil, and at intervals 

 gives rise to a comparatively large 

 leaf. This leaf has a long erect 

 petiole and a blade of four spread- 



PlG. 133.— A water-fem (Marsilia). 

 showing horizontal stem, witli 

 descending roots, and ascend- 

 ing leaves ; a, a young leaf 

 showing circinate vernation ; 

 s, 5, sporophyll branches ( ' ' spo- 

 rocarps "). — After Bischoff. 



Pig. 134. One of the floating water-ferns iSal- 

 mnia), showing side view (.41 and view from 

 above {B). The dangling root-like processes 

 are the modified submerged leaves. In .1, 

 near the top of the cluster of submerged 

 leaves, some sporophyll branches ("sporo- 

 carps") may be seen.— After Bischoff. 



ing wedge-shaped leaflets like a " four-leaved clover. " The 

 dichotomous venation and circinate vernation at once sua:- 

 gest the fern alliance. From near the base of the petiole 



