TilE (.lliEAT ClKiUl'S OK rTEUIlml'Il VTKS 



?,?A 



" four-leaved clover." The dicliotomous venation and cir- 

 cinate vernation at once suggest the fern alliance. From 

 near tlie base of the petiole another 

 leaf branch arises, in which the blade 

 is modified as a sporophyll. In this 

 case the sporophyll incloses the spo- 

 rangia and becomes hard and nut- 

 like. Another common form is the 





I iff \imA 



A 



!W)!i;i- 



\ 



n 



Fiii.303. A water-fern (.l/rn-.'-v/JTV Fir;. 304. One of tlu- llnjuiiiLf watcr-fcnis i.sV//- 



eliDWiny: lioriznntal stem, -with 

 depcendiiiy; roots, and asceml- 

 ing leaves ; a. a yonii,ix U'af 

 sbowinr; circinate vernation ; 

 -«,.T. sporophyll branehes ("spo- 

 rocarps"'). — After Bisciioff. 



riii'uC), show'infj side view (.1 1 and \iG\v from 

 above (7i). Tbe dangling root-like processes 

 are the nioditied submerged leaves. In .4, 

 near tbe top of the clnster of snbmerged 



lea\'es, some sporophyll branches ("si)oro- 

 carps "1 may be seen.— After Bi^choff. 



floating Siilri)ni( (Ficr. 304). The chief interest lies in the 

 fact that the water-ferns are heterosporous. As they are 

 lepto-poranc^iate they are thonirlit to have heen derived from 

 the ordinary leptosporan.ii'iate Ferns, which are homosporous. 



Equisetales (Ilnrsrtails or Srourina rnslies) 



219. General characters.— The twenty-five forms now rep- 

 resenting this great group belong to a single genus {Equise- 



