120 POLLINATION [CH. 
probable that cross-fertilisation ever occurs, since the 
paleze do not open, and the pollen falls on to the stigma 
direct; and in Leersia and 
the foreign Amphicarpum 
the spikelets are completely 
cleistogamous, those of the 
latter being on stalks close 
to the ground which push 
the flowers into the soil, 
where pollination and fruc- 
tification are accomplished. 
Hybrid grasses are by 
no means uncommon. To 
say nothing of the numerous 
cross-bred Wheats and Bar- 
leys, artificial hybrids have 
been raised between Wheat 
and Rye. In the Maize 
an astonishing number of 
selected cross-breeds have 
been obtained, and, among 
others, certain forms in 
which the seeds have a 
violet outer layer and a 
sugary endosperm, are found 
Fig. 37. Pollen-grains adherent to 
the papille of the stigma, on 
which they germinate, sending 
the pollen-tubes down between 
the cells. Kerner. x about 100. 
to transmit these characters to the resulting seed of a 
variety which would normally have produced seed with 
white outer layers and starchy endosperm, if the pollen of 
the former is used on the stigma of the latter. Such 
direct influences of the pollen are termed Xenia. 
