FERNS. 



341 



cell remains undivided. The cells develope into germinating filaments, bursting the 

 exospore in three directions ; these filaments then grow at their apex, and become 

 segmented by septa; only one of them however generally attains a more decided 

 development, the others soon assuming the form of hairs. In Hyfiieriophyllum tim- 

 bridge?jse the former frequently developes finally into a cellular plate ; but in other 

 species it forms a much-branched conferva-like protonema, on which flat prothallia 

 2 to 6 lines in length and |- to i^ in breadth are formed as lateral shoots. Each cell 

 of the filament may give rise to a branch which is given off behind the anterior 

 septum, and is at once separated by another septum. Some of these branches 

 continue to grow Hke the mother-shoot indefinitely, others end in becoming hairs; 

 a larger number are transformed into flat prothallia, but most develope into 

 root-hairs. Here and there the rudiment of a filamentous branch becomes con- 

 verted into an antheridium, or even into an archegonium. At the apex of the 

 flat prothallia spherical cells arise in Trichornanes mcisiim on marginal flask-shaped 

 cells : these must probably be considered as organs of propagation ; but the mar- 

 ginal cells of the flat prothallia may develope into root-hairs and new protonemal 

 filaments, and also into new flat shoots. The root-hairs are mostly short, with 

 brown walls, and produce at their end lobed attaching-discs or branching tubes. 



In the Polypodiaceoe and Schizaeacese the endospore developes into a short 

 articulated filamentous pro-embryo, at the end of which, even at an early stage, a 

 more or less considerable increase in breadth takes place ; a plate of tissue is thus 

 formed consisting at first of only one layer, which soon assumes a broadly cordate 

 or even reniform shape, and has its growing apex situated in an anterior depression. 

 Its apical cell forms two rows of segments right and left, by walls which are per- 

 pendicular to the surface, and from their further divisions the flat tissue is produced. 

 The power of rejuvenescence of the apical cell is, however, limited ; it ends in the 

 formation of a septum by which a new apical cell is formed, which then divides 

 by longitudinal walls, and thus forms a row of apical cells lying side by side 

 which occupies the bottom of the depression of the prothallium-disc, in the same 

 manner as in the thallus of Pellia. The root-hairs are all lateral structures, 

 springing in large numbers from the under- side of the posterior part of the pro- 

 thallium ; among them are the antheridia, which in this case are only rarely mar- 

 ginal. The archegonia are also produced on the under-side, but on a cushion 

 behind the anterior depression formed of several layers; in Ceratopteris several 

 cushions are formed bearing archegonia. 



Osmunda (examined minutely by Kny, and compared with the preceding, /. c.) 

 is distinguished in the first place from the Polypodiacese and Schizaeaceae by the 

 absence of the pro-embryo. The endospore undergoes divisions at the very com- 

 mencement of germination, which form a plate of tissue of which a posterior cell 

 is converted, as in Equisetaceae, into the first root-hair. The succeeding root-hairs 

 arise from marginal ceils and on the under-side of superficial cells of the prothallium, 

 the apical growth of which follows a similar course to that of Polypodiaceae. The 

 mid-rib consisting of several layers is characteristic of Osmunda, penetrating the 

 ribbon-like prothallium from the posterior end to the apex, and producing a large 

 number of archegonia on both sides. The antheridia spring partly from the margin, 

 partly from the lower surface with the exception of the mid-rib. 



