300 IIOFMEISTER, ON 



tudinal rows of cells. It may be asserted that the Equise- 

 taceae on account of the diaecious nature of their prothallia, 

 and the constant similarity of the structure of their arche- 

 gonia with that of the archegonia of the Rhizocarpese, 

 especially of Pilularia, form the transition from ferns to the 

 Rhizocarpeae. 



Male and female prothallia grow in the closest proximity, 

 their shoots often intermingling with one another. The 

 access to the archegonia, which is afforded to the sperma- 

 tozoa not only by every rain but also by every heavy dew, 

 is rendered still easier by the force with w r hich, on the 

 spontaneousopening of over ripe antheridia,*the spermatozoa 

 still enclosed in their mother-cells — are ejected. I found 

 in the canal of a recently impregnated archegonium mucila- 

 ginous masses closely resembling defunct spermatozoa 

 (PL XXXVIII, fig. 4). 



The first visible change in an impregnated archegonium 

 is the closing of the lower end of the canal, caused by the 

 horizontal expansion of the cells of its walls (PI. XXXIX, 

 fig. 4, PI. XL, figs.l — 8). This closing is accompanied by 

 the further multiplication of the cells of the tissue surround- 

 ing the central cell. These cells divide repeatedly by lon- 

 gitudinal and transverse septa ; the division is particularly 

 active in the cells of the epithelium-like layer which adjoins 

 the central cell. The impregnated germinal vesicle has in 

 the mean time become somewhat larger. Its nucleus has 

 disappeared, and a layer of finely granular protoplasm 

 lines its inner wall (PL XXXVIII, fig. 4). Now for the 

 first time — after the obliteration of the lower end of the 

 canal — the series of divisions commences by which the 

 embryo is produced. 



The germinal vesicle is first divided by a septum inclined 

 to the longitudinal axis of the archegonium. The two 

 halves are again immediately divided by transverse septa 

 at right angles to those just formed. Sometimes the upper 

 and sometimes the lower of the two first cells of the rudi- 

 mentary embryo takes the lead in this division (PL XXXVIII, 

 figs. 5, 6). 



* It is at this time only that the small delicate crown represented by Thuret 

 (' Ann. d. Sc. nat.,' iii S., vol. xvi, pi. 16, f. 1) is formed. 





