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LOTSY, CURRENT THEORIES OF EVOLUTION. 387 
demonstrated was diversity and nothing but diversity. Why then 
does he speak of variation? Because he has a creed, the firm 
belief that all scallops have descended from a single initial specimen, 
or from a pair of such and that scallops were wont to reproduce 
their kind faithfully, until, in some mysterious way, they changed 
their constitution, by a process, limited to living matter, which 
process was called: variation. There is, ofcourse, no doubt, that 
organisms do vary, that, for instance, part of the progeny of a 
particular kind of plants, raised under unfavorable conditions, has 
quite another aspect than another part, raised under favorable ones, 
so that the exhibit of scallop-shells in the New York Museum may 
illustrate variation, but this conclusion can not legitimately be drawn 
from the mere observation of differences, in as much as such 
observation is unable to reveal anything else than the existence of 
diversity. How easy it is to confound diversity with variation the 
following case, may show. A mexican shrub of the Composite-family: 
Parthenium argentatum was considered to be highly variable. A 
thorough investigation by Dr. MACALLUM of Continental in Arizona 
has revealed the presence of more than a thousand different types 
within this linneon, each of which proved, on cultivation, to be 
perfectly constant; the supposed variability, thus proved, on proper 
investigation, to be mere diversity. As a matter of fact mere obser- 
vation can never reveal variability. We all know that there was a 
time when it was considered possible to distinguish between 
variability and diversity by observation and registration only. If 
the observed differences could be arranged in such a way that they 
oscillated around a common mean. in other words that they gave 
a frequency-curve it was thought that reliable evidence of variation 
was obtained. The mere mentioning of the name JOHANNSEN is 
sufficient to remind you of the fallacy of this deduction, as you 
know that he showed how genotypically different types of beans, 
bought in the market, could be arranged in such a way that they 
formed an almost ideal frequency-curve. 
Consequently we can observe diversity, but we have to study 
experimentally, whether observed deviations from the form which 
we consider as the type of a species (which, as a rule, means nothing 
but the most frequent form or even merely the first discovered 
form within that species) are variations or not. 
