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they would need no especial devices to insure their dryness, but they 
would have only a very remote prospect of germinating, and when the 
spores are formed, when they do have a chance to germinate, they would 
be very unlikely to become dry enough to scatter if borne in the position 
of the vegetative frond. 
To summarize : dimorphism, whether merely begun, or highly devel- 
oped, whether a character of whole fronds or of their parts, has in all 
cases the object of permitting the proper dryness of the mature sporangia 
without an improper desiccation of the vegetative structures. This is 
done by merely raising the reproductive structures farther above the 
substratum; or (rarely) by special structural devices, such as notched 
margins; by a restriction of the assimilating surface of the reproductive 
frond or region, so that it may be sacrificed in emergency; or by a more 
complete elimination of the vegetative structures in constitutionally 
ephemeral fertile fronds. 
IV. TAXONOMY. 
In discussing the San Eamon ferns from the systematic side, I shall 
hold myself chiefly, but not absolutely, to the local material, and in using 
this I shall be contented with pointing out some characters observed 
in groups which locally are notably well represented, and in suggesting 
briefly the probable genetic affinities of these ferns. 
The past decade has been that of the greatest advance in systematic 
pteridology, because it has seen the general and surely the final aban- 
donment of the idea that any single structure is of equal importance in the 
natural classification of all groups of ferns, or is even in gvery case of any 
value at all. The indusia are very useful in the proper characterization 
of many genera and tribes, but are not always of certain specific value 
in N ephrodium , or Aspidium. The shape of the sorus is sometimes of 
generic or even tribal value as a diagnostic character, but is variable in 
some species — and individuals — of Aspidium, Athyrium, and Phymatodes. 
In a single species of Leptochilus, L. lanceolatus Fee, the sporangia may 
be in distinct sori, or may cover the whole nether surface. The veins 
are sometimes free, sometimes anastomosing, on single individuals of 
Schizoloma fuligineum and Polypodium calif ornicum. Dryostachyum 
splendens, descended from ferns with articulate stipes, has sometimes 
evident vestigial articulations, sometimes apparently none; yet each of 
these characters, presence of indusia, shape of sorus, venation, and 
articulation of stipe, has sometime been held to be a fit basis for the 
initial or general classification of all Polypodiaceos. 
Since all of these characters, and all other real characters are, phylo- 
genetically (not, so far as we know, ontogenetically), adaptations to the 
environment and since the family is an old one and environments not only 
change, but are seldom found to be sharply differentiated, and the dis- 
semination of spores is unceasing, it would be very wonderful if there 
