61 
they would need no especial devices to insure tlieir di-yness, but they 
wouhl liave only a very remote prospect of germinating, and when the 
^ spores are formed, when tliey 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 liighl}' devel- 
oped, whether a character of wliole fronds or of their partb, lias in all 
eases the object of permitting tlie proper dryness of tlie mature sporangia 
without an improper desiccation of the vegetative structures. This is 
done by merely raising the reproilnctive structures fiirther above the 
■ substratum; or (rarely) by special structural devices, such as notched 
margins; by a restriction of the assimilating surface of tlic reproductive 
frond or region, so that it may be sacrificed in enuTgency; or by a more 
complete elimination of the vegetative structures in constitutioually 
ephemeral fertile fronds. 
IV. TAXONOMY. 
In discussing the iSan Ramon ferns from thi; systematic side, 1 shall 
hold myself chiefly, but not absolutely, to the local juaterial, and iu using 
this I shall be contented with pointing out souic characters oltscrved 
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 tlie geuoral and surely the final al)an- 
donmcnt of the idea that any single structure is of equal importance in the 
natural classification of all groups of ferns, or is even in every case of any 
value at all. The indusia are very useful in the proper charaeterixation 
of many genera and tribes, but are not always of certain specific value 
in Nephrodium, 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, Afhjjnuni, and Phi/mafodes. 
Inn single species of Leptochihis, L, lanceolahts Fee, the sjiorangia may 
be in distinct sori, or may cover the whole nether surface. Tlie veins 
are sometimes free, sometimes anastomosing, on single individuals of 
Schizoloma fuVujincum and Pohjpodium californicum. Dnjosiachyvm 
spIendoKs, descended from ferns with articulate stipes, has sometimes 
evident vestigial articulations, sometimes apparently none; yet each of 
these characters, presence of indusia, shape of sums, venation, and 
articulation of stipe, lias sometime been held to be a fit basis for the 
initial or general classification of all Pohjpodmcem, 
Since all of these characters, and all other real characters are, ])hylo- 
genetically (not, so far as we know, ontogenetieally), adaptations to the 
environment and since the family is an old one and environments not only 
chan^'-e, but are seldom found to be sharply difTcrentiatcd, and the dis- 
semination of spores is unceasing, it would be very wonderful if there 
