CHAPTER IV 

 STEMS 



Development of Shoot System. — When a grain of wheat 

 germinates, the primary root is the first to appear. Very 

 soon two lateral roots make their appearance, forming a 

 primary root system of three roots. Also, the young stem 

 (Fig. i) elongates, and there is formed the first shoot 

 system of the plant. Elongation of the stem continues by 

 growth at the tip, where the cells are young and active. 



It is observed that the stem is divided into sections (inter- 

 nodes) fFig. 25). The nodes, the enlarged joints between 

 the internodes, give rise to leaves, and if we follow the wheat 

 plant through its life, we observe that the stem terminates 

 in an inflorescence (flower cluster). Now, in addition to the 

 one main stem that arises as a prolongation of the embryonic 

 stem in the seed, branches arise from the lower nodes. These 

 branches arise in the axils of the lowermost leaves, in most 

 cereals. In cereals, this branching is known as "stooling" 

 or "tillering." Common cereals invariably produce a num- 

 ber of tiUers or branches from the primary stem, and these 

 in turn other tillers (lateral branches), so that under favorable 

 conditions several dozen culms may result from a single seed. 

 In the wheat plant, two or three weeks old, three or four 

 buds (young stems) may be found, one in the axil of each 

 leaf. Tillering results from the outgrowth of these lateral 

 buds. Hence, as a result of the elongation of the main 

 growing point, and of the lateral growing points into lateral 



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