THE FERNS 



533 



certain ferns closely related to tlie aliovc more nearly resembles 

 that of Anthoceros, and is holophytic, as we may suppose to have 

 been the case with the orif>;inal feru-ancestor. When we compare 

 the sporophytes of an adder-tongue and a horned liverwort, how- 

 ever, so many striking differences appear, that it may at first seem 

 hopeless to think of homologizing the parts? Indeed, we have in 

 ferns true leaves, stems, and roots, no trace of which appear in any 

 liverwort. But we have sporangia in both, and in the growing zone 

 of Anthoceros we have a cjdindrical meristematic organ suggesting 

 possibilities of much further differentiation. If the sporangium of 



Fig. .358. — -Grape-fern. A, gametophyte (prothallus) cut vertically to 

 show the antheridia (an), the archegonia {ac), and the pseudo-roots (w), 

 ^{'-. B, lower part of a young sporophyte dug up in September, cut 

 vertically to show the stem (si) and leaves (b, b', b"), 'f. (Hofmeister.) 



Fig. 3.59. — -Adder-tongue. Upper part of spore-bearing division of leaf ("), 

 cut vertically to show the tip (s), the spore-cavities (.sp), the places (r) 

 where a slit is formed to free the spores, and the woody strands or fibro- 

 vascular burulles (g) which strengthen and conduct sap. (Sachs.) 



Anthoceros were enlarged and instead of elaters produced sterile 

 tissue between groups of spores forming two rows on either side of 

 the columella, the resulting organ would be a flat spike of sporangia 

 like that of Ophioglossum (Fig. 359). What may have happened 

 is that in very ancient times, before the age when coal plants flour- 

 ished, a liverwort something like an Anthoceros did evolve a root 

 from the lower end of its growing zone, which made possible an 

 expansion of the green tissue above, while this in turn helped to 

 bring about the formation of two rows of globular sporangia making 

 a flat cluster as already described. Such an expanded member 



