691 
Cross-fertilisation of Cereals. 
2. T. Spelta (L.), which has a loose four-sided ear, the grains 
do not fall out in threshing, and the empty glumes are truncate 
with a blunt middle tooth. 
3. T. dicoccum (Schrank), with ears dense and two-sided, the 
grains do not fall ont in threshing, the empty glumes taper and 
have a sharp middle tooth. 
4. T. vulgare (Vilh), with compact ears, the grains fall out 
when threshed, and the empty glumes are keeled on the upper 
half. 
5. T. turgidum (L.), with dense four-sided ears, the grains fall 
out when threshed, the empty glumes are keeled to the base, 
and the grains are short, thick, and blunt. 
6. T. durum (Desf.), with dense long-awned ears, the grains 
fall out when threshed, the empty glumes are keeled to the 
base, and the grain is long, narrow, and very hard or flinty. 
7. T. polonicum (L.), with long, compressed ears, long 
papery glumes, and long and narrow, grains. 
The question as to how many species are represented in 
these seven forms is very differently answered. Blomeyer in 
his recent work on cultivated plants considers that they repre- 
sent but the single species T. sativum (L.) Hackel, who is our 
first living authority on grasses, considers T. monococcum (L.) an 
independent species. Besides the obvious characters by which 
it is distinguished, the fact that it has not been possible to 
produce fertile hybrids between this plant and any of the 
varieties of T. sativum (L.) justifies its separation as a species. 
T. polonicum (L.) he also treats as a species, but as fertile plants 
have been obtained by crossing with the varieties of T. sativum 
(L.), he suggests that it may have originated under cultivation, 
and consequently not be a true species. Bentham recognised 
T. monococcum (L.) and T. Spelta (L.) as independent species. 
The axis of the ear is jointed in both these forms, so that when 
threshed the ear breaks up into fragments at the joints. As 
this jointed ear is found in many of the wild species of the 
genus Triticum, it may represent a primitive characteristic 
which has not disappeared in these two forms under culture. 
This would point to T. Spelta (L.) as the nearest living represen- 
tative of the original T. sativum (L.) That it is only one of the 
forms of this species seems to be established by the ease with 
which it is crossed with the other forms. 
It must be apparent, then, that in seeking improved varieties 
of wheat by crossing we cannot use T. monococcum (L.), and we 
should not use T. polonicum (L.), but that all the other varieties, 
seeing they are but forms of one species, are available for this 
purpose. 
z z 2 
