246
THE ESSEX NATURALIST.
had replaced the ζείαι in Greece before they replaced far in
Italy, may be surmised from what Xenophon had to say of the
rude and inhospitable Mosynaeci, whose acquaintance the
retreating Ten Thousand made as they approached the Euxine :
one mark of the backward state of this tribe was that ζείαι
the Emmer, was still their staple cereal. Theophrastus,
whose πυρός excluded ζείαι and τίøη and όλυρα, and
therefore no longer meant what its linguistic equivalent far
implied, knew and named nine distinct sorts of πυρός which
scholars have tried to identify, though with indifferent success.
This is hardly surprising : as White of Selborne once said,
classical writers "did not attend to specific differences like
"modern naturalists."
There is only one very limited area in which the Indian
Dwarf Wheat, Club Wheat and Bread Wheat occur in culti-
vation together. This is in North-West India and Afghanistan :
in that area, therefore, Prof. Vavilov finds the 'centre of diversity'
which supplies the clue to the 'centre of origin' of this group of
wheats with 21 pairs of chromosomes, just as he finds in Abyssinia
the ' centre of origin' of the more modern derivates of Emmer
with 14 pairs of chromosomes.
Mr. Haldane has told us that the cytologist has learned from
experience to anticipate that the progeny of hybrids between
'races' with an odd and 'races' with an even basic haploid
number of chromosomes will be more or less sterile, because
there is a chromosome which cannot pair. This is certainly the
case with hybrids between the Locular with 7 pairs and Emmer
with 14 pairs, and is also the case with hybrids between the
Locular and the 'races' of the group to which Macaroni Wheat
belongs. It is, as a rule, equally the case with hybrids between
'races' of the Macaroni Wheat group with 14 pairs of chro-
mosomes, and 'races' of the Bread Wheat Group with 21 pairs.
But, as Prof. Percival points out, there may be an exception
to the rule, because Rivet Wheat, with 14 pairs, shares certain
morphological features peculiar to the European varieties of
Emmer, with certain morphological features peculiar to Club
Wheat, which has 21 pairs. Rivet Wheat is found from Portugal
to Transcaucasia where Emmer and Club Wheat are present, but
is absent from the Orient, from India and from China, where
cither Emmer or Club Wheat, or both, are absent.