ch. vi] Key to Grass "Seeds" 39 



just below the apex (sub-terminal), or near the middle of the 

 palea (dorsal awn). It may be either straight, bent, twisted, 

 smooth or barbed. 



A careful examination of these points, together with the 

 size of the "seed," the shape and relative size of the rachilla, 

 the position of hairs, etc. will soon enable the student to dis- 

 tinguish most grass "seeds." In the key O.P. indicates the 

 outer palea and I.P. the inner palea. The pages given refer to 

 the fuller description. 



9 o 



a 



c 



& 







Figs. 24 and 25. Types of Staioh Grains. 



Fig. 24. Simple grains from endo3perm of Agropyrum repens. x about 350. 

 Fig. 25. Compound grains from endosperm of Festuco, pratensis. x about 350. 



It may here be noted that the starch grains of the endosperm 

 also afford characters which are useful aids to the identification 

 of species. The size, form, and structure of these are often very 

 different in the different genera (see Figs. 24 and 25). In Maize, 

 Wheat, Barley and Rye, and also in the genera Panicum, Agropyrum 

 and Elymus they are simple and either rounded or polyhedral in 

 form. In all other British genera compound grains occur. Further 

 details cannot be given here. See Bibliography, Nos. 10 and 35. 



Key to British Grass "Seeds." 



Group I. "Seeds" distinctly awned. 



A. Awn terminal, i.e. the O.P. tapers off into an awn. 



1. "Seed" consisting of the spikelets usually . united in 

 threes: Hordeum. 

 (a) Awn exceeding twice the length of the O.P. 



H. murinum (Fig. 118), empty glumes of central 



spikelet dilated and fringed (common) (p. 109). 



H. sylvaticum, glumes only slightly dilated ; those 



