GRASSES OF IOWA. 71 



escence fall off with the fruit. If the spikelet is many- 

 flowered and every flower ripens its fruit, then its axis breaks 

 into as many pieces as there are fruits, and every piece carries 

 a floral glume and palea. If the spikelet is one- flowered, the 

 axis of the spikelet may separate above the empty glume, so 

 that the floral glume and the palea fall off with the fruit 

 (Agrostese); or it may divide below the empty glume, and the 

 spikelet fall off as a whole (Panicese, Andropogonese, etc.). If 

 the spikelets form a spike or a raceme, it frequently happens 

 that the latter divides so that one spikelet falls off with each 

 joint (many Andropogonea? and Hordeae); short spkes {Triti- 

 cum ovatum Godr.) fall from the culm as a whole. All these 

 arrangements are necessary for the distribution of the seed; 

 they are lacking (with two exceptions) in all cultivated cer- 

 eals, but are present, on the contrary, in all native races of 

 the same species, so far as these are known. Since these 

 arrangements are very disadvantageous for the complete gath- 

 ering of the fruit, varieties whose axes are less or not at all 

 articulated will be preferred in culture, and will be finally 

 fixed by natural selection. " 



Seeds to be disseminated by the wind must be sufficiently 

 light. Surrounding the fruit are bracts, which diminishes the 

 specific gravity. Hordeum jubatum, and Agrostis are carried by 

 wind because of their lightness. In many grasses copious hairs 

 are developed either as parts of the sterile glume or parts of 

 the axis. In Audropogon the rachis or both rachis and the 

 steriJe flowers are provided with long hairs. In Phragmites 

 the base of the flowers are silky villous and with a conspicuous 

 silky-bearded rachis. 



In Calamagrostis the callus of the flowering glume is pro- 

 vided with short or long hairs. In Poa the principal veins 

 of the flowering glume are cobwebby (figure 36). The seeds 

 readily adhere to woolly objects, or they maybe carritd by 

 the wind. 



The beautiful European Stipa pennata, and our variety, neo- 

 mexicana, are well adapted for wind dissemination. Its long 

 plume makes it easy for the wind to carry. 



The wind, however, acts in other ways. The Australian 

 Rolling Spinifex forms a large round head. This breaks away 

 and rolls over the dry sands of Australia until it is carried to a 

 dry place, when it expands and soon takes root. In tickle 

 grass {Panicum capillare) the whole infiorescence breaks away 



