THE STEMS 65 



lengthens into a thin erect rhizome which pushes the terminal bud up- 

 wards through the soil. 



This rhizomatous portion of the stem is from -6 mm. to i mm. in 

 diameter, much thinner than the aerial straws of the plant, and is usually 

 the second internode of the epicotyl. When grains are sown at a depth 

 of four inches or more, the second and third and sometimes other inter- 

 nodes above these often lengthen to form part of the rhizome (Fig. 61) : 

 at depths of three inches or less, the rhizome usually consists of the second 

 internode only. 



In plants grown from grains sown three inches deep, the first, second, 



r, 



FIG. 59. Young plants with shoots at the " tillering " node, o, Scutellum ; r, seminal 

 roots ; r' and a (in 2), adventitious roots ; x, rhizome ; a (in i), shoot in axil of cole- 

 optile ; c, shrivelled coleoptile ; n, prophyll of first shoot; 5, leaf-blade of ist leaf; 

 T> T> f> and ^, ist, and, 3rd, and 4th leaves of primary axis ; p, prophyll of first shoot. 



and third axillary buds of the main stem remain dormant or give rise to 

 weak shoots, the fourth lateral bud being the first to produce a strong shoot. 



The third axillary 'bud is generally the first to grow strongly when 

 grains are deposited two inches in the soil, the second developing most 

 rapidly when the grain is sown one and a half inches down. 



The bud in the axil of the first foliage leaf grows out immediately 

 when the grain is placed nearer the surface of the soil. 



The length of the rhizome varies with the depth at which the grains 

 are deposited. When the latter are placed on the surface, or less than an 



F 



