22 SEEDS : STRUCTURE AND GERMINATION 



examples which may be considered typical of the monocotyledons 

 and easily obtainable. 



To this class, however, belong all the grasses, but their seeds 

 and embryos are so different in many respects from those of the 

 onion that it is necessary to examine one of them in detail. 



Wheat. — A wheat grain, which may be taken as an example, 



is not a seed, but a kind of nut with a single seed within it. 



The seed grows in such a way as to completely fill up the in 



terior of the nut, and become practically united with its inside 



wall. The embryo occupies only a 



small part of the grain, the rest being 



taken up by the floury endosperm of 



the seed (2, Fig. 7). 



The embryo is easily seen at the 

 base of a soaked grain on the side 

 opposite the furrow. When removed 

 it has the appearance seen at i, Fig. 7. 

 The part of it which lies close up 

 to the endosperm is a flattened 

 somewhat fleshy shield-shaped struc- 

 ture called the scutellum (sc) ; attached 

 to the front of the scutellum is the 

 plumule (/), consisting of a bud 

 formed of an extremely short stem, 

 upon which are sheath -like leaves 

 enclosing each other. The embryo 

 generally possesses three roots, the 

 middle one seen at r^, Fig. 7 being 

 Fig. s.-i. Seedling wheat plant, the primary root. They are all com- 

 ^ F^st^heathTng^ie'arof^Sm^a'; Pletely enclosed by a sheath which 

 'h:'firsVgie''en1e{f /^ergel?" >s continuous with the scutellum, and 

 are consequently not visible from 

 outside ; their position, however, is marked by three projecting 

 bosses. The sheath round the roots is termed the coleorhiza {co), 



