332 Evolution in the Plant Kingdom. 
the fern in vain for any evidence of sex-organs, for he only 
knew of this prominent asexual phase, and in his despair con- 
signed the group to “Cryptogams,” “hidden sexuality.” The 
asexual spores (borne, you may remember, upon the leaf-struc- 
tures of the fern) develop, of course, into the sex-phase; but 
that is so small and hidden among the mold in which the 
spore has fallen, that it may well escape observation. It is 
simply a minute flat disk-like body, with vegetative cells and 
root-like processes enough to make it able to live long enough to 
accomplish its function of sex-reproduction. But it bears the sex- 
organs, produces the sex-spore, and from it there arises the beau- 
tiful or stately asexual plant. The reduction of the sex-phase 
could go no further than this, and at the same time compel it to 
make its own living from soil and air. If any more reduction be 
made, the sex-phase cannot be organically separated from the 
other, but must depend upon it for elaborated food. 
By this means the utmost possible reduction could be reached, 
and we must expect this to be the next step in advance. For 
instance, the asexual spores of the fern are scattered over the soil. 
From them springs the reduced sex-phase, known as the prothal- 
lium, and capable of independent existence. Any further reduc- 
tion, which would make it incapable of independent existence, 
would necessitate that the asexual spore be not separated from the 
asexual plant, but developed into the prothallium upon it so as to 
receive elaborated nourishment. The reason why a prothallium 
cannot be indefinitely reduced, and still retain the power of inde- 
pendent existence, is not far to seek. It is on the same principle 
that a small battery cannot work an indefinite amount of wire. 
The formation of high-grade reproductive cells is an exhaustive 
work, and it would require more than a few cells to manufacture 
such an amount of highly organized substance from crude material. 
Hence we reach a point, beyond which it would be a physical 
impossibility to reduce the prothallium, without arranging tO 
supply it with material already highly organized. 
Remembering, then, that from the sixth group, represented by 
ferns, higher rank is to be marked by a reduction of the sex-phase 
or prothallium, which finally cannot be separated from the asexual 
plant, let us note a new phase of differentiation which begins to be 
prominent in the upper members of the sixth group, and continues 
