THE CEDAR APPLES OF THE UNITED STATES. 
139 
spores of y^cidium Berberidis germinate on grasses, producing rust 
{Uredo), and finally Fuccinia. We must admit that in all grasses 
there is an undoubted tendency to produce the Uredo and Fuccinia, 
although many miles distant from a barberry, or even in countries 
where no barberry is known. Also, if any parasite at all is to be 
found on the living barberry, lih^Fcidium Berberidis. Supposing 
that, experimentally, the Fuccinia is sown on the barberry, and 
the result is the production of jBcidium Berberidis, what does this 
prove ? Absolutely nothing ! No one can possibly contend that 
it proves anything. Sow the spores of Uredo filicum on leaves of 
the gooseberry, and the result may be the production of jEcidium 
Grossularice. What is the inference ? Absolutely nothing ! In 
the one case, as in the other, the chain is broken. The toad spawn 
produces a newt or a lizard. It is not like producing like, and 
hence the evidence must be indisputable, and not problematical. 
There must be stronger evidence necessary to establish the fact of 
the development of 2^0. ,uEcidium from a Uredo spore than of an 
jF.cidium from an Mcid.iwm spore. In like manner there must be 
stronger evidence of a lizard being developed from the ova of a toad 
than from the ova of a lizard. Is there stronger evidence that 
the Fuccinia sown on barberry really produces an jFcidium than 
would be required to prove that the .^cidium spores produced the 
^cidium ? It cannot be forgotten, it must not be ignored, that 
the parasite of the barberry naturally is the very one which is 
said to be produced experimentally. We contend that it would 
have made its appearance even had not the Fuccinia spores been 
sown ; that the supposed cause is not a true cause ; that the true 
cause acted in opposition to the supposed cause. And what evi- 
dence is there to oppose to our allegation ? For the sake of argu- 
ment (as it applies to all those cases in which one supposed con- 
dition of a Uredine is passed on plants of one genus, and the ulti- 
mate condition upon another), we have an undoubted right to 
demand — not that the theory should be assumed, but that the fact 
should be incontrovertibly established — that Fuccinia spores sown 
on barberry produce Mcidium Berberidis ; that ^cidium Ber- 
beridis would not have been produced on that plant but for the 
sowing of the Fuccinia. The same argument applies to the grasses 
and the ^cidium spores. Sow spores of the JEcidium upon 
young wheat, protect it from all other influences, and the result is 
the common Uredo, succeeded by Fuccinia. This may well be the 
case, and yet the spores of the yEcidium may not have produced 
the Uredo. It is useless repeating the argument again. Every 
blade of wheat gives evidence of the presence of the Uredo with- 
out any sowing of ^cidium ; and why multiply causes ? If the 
sowing of the germs of one kind of parasite upon a host results 
in the production of another kind of parasite, and not the one 
sown, then the evidence must be produced in an unbroken chain, 
and must be positive, and not problematical, or the assumed cause 
cannot be accepted as a true cause, It is useless to call people 
