ten or a hundred times, as many plants must be examined to secure them,
but species with absolutely pure dicotylous seeds are very rare.

The second phase of the experiment, however, is not so promising. Some
species are rich, and others are poor in this anomaly. This difference
[419] often indicates what can be expected from further culture. Stray
tricotyls point to poor species or half-races, while more frequent
deviations suggest rich or double-races. In both cases however, the
trial must be made, and this requires the isolation of the aberrant
individuals and the determination of their hereditary percentage.

In some instances the degree of their inheritance is only a very small
one. The isolated tricotyls yield 1 or 2% of inheritors, in some cases
even less, or upwards up to 3 or 4%. If the experiment is repeated, no
amelioration is observed, and this result remains the same during a
series of successive generations. In the case of _Polygonum
convolvulus_, the Black bindweed, I have tried as many as six
generations without ever obtaining more than 3%. With other species I
have limited myself to four successive years with the same negative
result, as with spinage, the Moldavian dragon-head, (_Dracocephalum
moldavicum_), and two species of corn catch-fly (_Silene conica_ and _S.
conoidea_).

Such poor races hardly afford a desirable material for further
inquiries. Happily the rich races, though rare, may be discovered also
from time to time. They seem to be more common among cultivated plants
and horticultural as well as agricultural species may be used. Hemp
[420] and mercury (_Mercurialis annua_) among the first, snapdragon,
poppies, _Phacelia_, _Helichrysum_, and _Clarkia_ among garden-flowers
may be given as instances of species containing the rich tricotylous