140 GERMINATION, GROWTH, TISSUE TENSION. 



178. Maize Grain. Get some Maize " seeds," also a 

 " cob " (female inflorescence) ; the seeds of the White 

 Horsetooth variety are much better (being larger and 

 more regular in shape) than the ordinary Indian Corn. 



(a) In a young cob note that the thicker end of the 

 young grain (ovary) bears a long feathery stigma; the 

 ripe grain is a one-seeded fruit, differing from an ordinary 

 achene in having pericarp and seed-coat fused together to 

 form the " husk." 



(5) In a soaked grain note the oval patch on one side, 

 indicating the position of the embryo ; with knife or 

 forceps catch at the pointed end of the grain and tear off 

 the thin tough skin (husk) and note the two appendages 

 fixed to the middle of the oval patch the free tip of the 

 plumule is towards the broad end and that of the radicle 

 towards the narrow end of the grain. 



(c) Lay the grain on the table with the embryo upper- 

 most, and make a clean slice down the middle of the 

 plumule and radicle ; note that these organs are attached 

 to a shield- shaped structure the scutellum which pro- 

 jects into the grain and runs obliquely across its interior. 

 Make sure of the general structure and relationships of 

 these three parts of the embryo ; dissect the plumule and 

 radicle with needle or knife, noting that the former con- 

 tains rolled-up young leaves within a sheath, while the 

 latter is a solid body also within a sheath. 



(d) To see the form of the scutellum better, (1) cut 

 transverse sections of the grain at different levels ; (2) re- 

 move the whole embryo from a well-soaked grain ; (3) cut 

 a grain longitudinally and smear the cut surface with 

 iodine, this brings out in sharp contrast the brown-stained 

 embryo (radicle, plumule, scutellum) and the blue or 

 almost black-stained starch-bearing region (endosperm). 

 Also treat with iodine the series of transverse sections of 

 the grain. 



179. Wheat Grain. The general structure is the same 

 as in Maize. In a soaked grain note the deep furrow 

 down one side, the small embryo at one end of the op- 



