EXPLANATION OF PLATE XXI. 



. (1) Upper part of fertile plant of E. limosum ; (2) one of 

 the shield shaped scales or receptacles of the spike, with the six sporangia 

 underneath, enlarged; (3) same seen from below, discharging the spores; 



(4) a magnified spore with the club-shaped filaments spreading; and 



(5) the same with the filaments coiled up. 



LYCOI'ODIUM. Plant of L. C'arolinianum, and (1) a magnified scale of 

 the spike removed, with the sporangium in its axil, discharging powdery 

 spores. 



SELAGINELLA. Plant of S. rnpestris ; ( 1 ) part of a fertile spike, enlarged ; 

 (2) scale from the upper part of it, with its sporangium, containing innu- 

 merable powdery spores; (3) scale from the base, with its sporangium 

 containing few large spores; and (4) three large spores. 



ISOETES. (1) I'lant of I. lacnstris ; (2) spororarp containing the minute 

 spores, cut across, enlarged ; (5) same divided lengthwise; (3) sporocarp 

 with the large spores, divided lengthwise; and (4) three large spores 

 more magnified. 



A/I >LI,A. (1) I'lant; (2) a portion magnified, with conceptacles of both 

 kinds; (3) the macmsponc one, more magnified; (4) the microsporic 

 one, more magnified ; (5) the same hurst open, showing the stalked micro- 

 sporangia; (<;) one of the hitter more magnified; (7) another bursting; 

 and (s) three masses of microspores beset with glochidiate or barbed 

 bristles. 



