434 BRITISH FLOWERING PLANTS chap. 



The seeds are not free, but are combined with the 

 wall of the ovary, thus forming a one-seeded fruit, 

 known as the " grain." The embryo is outside the 

 endosperm, not within it. 



The dissemination of the seeds is .provided for in 

 several ways.-" Sometimes they are very minute, as, for 

 instance, in Eragrostis ; generally, however, when 

 leaving the plant they carry with them parts of the 

 spikelet, which act as a balloon. In the quaking grass, 

 Briza, the glumes fulfil this function, and the same is 

 the case with species of Poa, Dactylis, Holcus, Festuca, 

 and Phalaris. In many cases the awns attach them- 

 selves to animals ; and in some the dissemination is due 

 to hygroscopic movements. 



Perhaps the most remarkable case is that of a 

 South European species, Stipa pennata (Fig. 350), the 

 structure of which has been described by Vaucher, 

 and more recently, as well as more completely, by 

 Francis Darwin. The grain is enveloped in the per- 

 sistent glume which is continued below into a sharp 

 point, and bears stiff short hairs pointing backwards. 

 The upper end is produced into a fine twisted cork- 

 screw-like rod, which is followed by a plain cylindrical 

 portion, attached at an angle to the corkscrew, and 

 ending in a long and beautiful feather, the whole being 

 more than a foot in length. 



The long feather no doubt facilitates dispersion by 

 wind ; eventually, however, they sink to the ground, 

 which they tend to reach, the fruit being the heaviest 

 portion, point downwards. So the fruit remains as 

 long as it is dry ; but if a shower comes on, or when 

 the dew falls, the spiral unwinds, and if, as is most 

 probable, the surrounding herbage or any other ob- 

 stacle prevents the feather from rising, the fruit 

 itself is forced down and so driven by degrees into the 

 ground.^ 



' Hildebrand, "Uberd. Verbreitungsmittel der Gramineen Friiohte," .BoJ. 

 Zeit. 1872. 



'■' Avebury (Lubbock), Flowers, Fruits, and Leaves, p. 90. 



