120 



POLLINATION 



[CH. 



probable that cross-fertilisatioii ever occurs, since the 

 paleae 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 Nvhich 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 



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. 



Fig. 37. Pollen-gi-ains adherent to 

 the papilliB of the stigma, on 

 which they germinate, sending 

 the pollen-tubes down between 

 the cells. Kerner. x about 100. 



