HOOKER LECTURE, I9I7. j 115 
should always be prepared for this. But usually they bear the relation of 
one extreme being relatively primitive, and the other relatively advanced. 
Such a conclusion, based on comparison, should whenever possible be 
checked by reference to the Fossil Record. Thus with a high degree of 
certainty that which is archaic may be distinguished from the more modern 
type, in respect of the character in question. 
A good illustration of the effect of the Paleontological check is found in 
the Filicales in respect of the type of sporangium. Von Goebel, in 1881 
(Bot. Zeit. p. 717), distinguished the more massive types of sporangium seen 
in the Ophioglossacez and Marattiacee as Eusporangiate ; while the more 
delicate types characteristic of the Polypodiacew were styled Lepto- 
sporangiate. Both are Filical types. Do they stand to one another as 
relatively primitive, and relatively advanced ? If so, which was the earlier ? 
I had written in 1889 (Ann. of Bot. iii. p. 305) a paper on * The Com- 
parative Examination of the Meristems of Ferns as a phylogenetic study.” 
All their meristems were shown to exhibit a parallelism with the sporangia 
in point of complexity. So that the difference between the Eusporangiate 
and the Leptosporangiate is really a difference of organization of the whole 
plant. Influenced by the general opinion of the time,—itself based on 
the assumed affinity of the Hymenophyllacez to the Mosses,—I then held 
the simpler Leptosporangiate type of organization to be the more primitive. 
But here came in the value of the Palzontological check. Stimulated by a 
paper of Professor Campbell, as cogent as it is brief (Bot. Gaz. vol. xv. 
Jan. 1890), the question was re-examined in the light of the fossil evidence. 
The virtual absence of Leptosporangiate Ferns from the Paleozoic, and the 
prevalence of the Eusporangiates at that period led to the inversion of 
the series (Ann. of Bot. vol. v. 1891, p. 109)—a position now generally 
accepted. Sporangial structure, which is an index of a bulky organization 
and complex segmentation of all the parts in certain types, and of a less 
bulky and complex construction in others, may accordingly be taken as a 
criterion. As exemplified by Fern sporangia, the more bulky Eusporangiate 
type is the more primitive, the less bulky Leptosporangiate type is relatively 
advanced. 
How far this will serve as a real index of their general organization is 
shown by the comparison between the sporangia and antheridia of the same 
plants, first instituted by von Goebel. It is found that where the sporangia 
are large and thick-stalked, or even sunken as in Ophioglossum, the antheridia 
are relatively large and are sunken too ; while in the Leptosporangiates, with 
their smaller sporangia and long stalks, the antheridia are also stalked and 
relatively small. The comparison even extends, though not with numerical 
accuracy, to the numbers respectively of spores and of sperms. Where the 
number of spores per sporangium is large, as in the Eusporangiate Ferns, 
the spermatozoids are also very numerous in each antheridium: in the 
