66 



THE WHEAT PLANT 



inch below, the rhizome is scarcely visible, being rarely more than two or 

 three millimetres in length ; at greater depths it lengthens proportion- 

 ately in such a manner that the plumule of the young plant produced 

 from a grain sown at any depth between one and three inches is lifted up 

 to within an inch or less of the surface (Fig. 60). 



When the primary bud has reached this point, the rhizomatous inter- 

 node ceases to lengthen, and the succeeding internodes of the plumule 

 remain short. 



During autumn and spring, however, the primary axis continues to 



123 456 



FIG. 60. Wheat seedlings from grains sown at depths of 1-6 inches. Note extent of 

 tillering, length of rhizome, and number and length of adventitious roots from the 

 first (tillering) node. (About half natural size.) 



grow very slowly, and, at the same time, in the axils of its leaves buds are 

 formed which expand into short secondary stems ; the latter also bear axil- 

 lary buds which are capable of developing in a similar fashion into branches 

 of the third order, and so on. Thus, from the primary bud of a single 

 wheat grain, a large number of stems may be produced, which remain very 

 short until April, at which date they usually begin to expand, the strongest 

 of them ultimately growing out into straws each with its terminal ear. 



The production of these numerous shoots with unexpanded inter- 

 nodes, which takes place near the surface of the soil, is known as the 

 " stooling " or " tillering " of the plant ; it is the normal process of 

 branch formation in cereals and grasses generally. 



The depth at which " tillering " or " stooling " begins, that is the 



