GR()\\'TH OF STEMS 



43 



moisture from within. Being smooth, it afl'ords no place for the 



lodgment of smut spores. Insects find difficulty in inserting their 



sucking mouth into these parts. 



(2) The woody wall, which is really a layer consisting of a close 



union of a great number of fibro-vascular bundles. In the small 



grains and grasses, this woody 

 wall is the only supporting 

 structure in the stem. From 

 each node, where a leaf grows 

 out, a number of these bundles 

 leave the wall to extend into 

 the leaf to feed it. The more 

 rank the growth, the greater 

 is the number of these bundles 

 in the wall, 



(3) The pith IS composed 

 of parenchyma cells and fills 

 the center of a corn stem. With 

 a given weig'ht of material, a 

 hollow column is stronger than 

 a solid one in withstanding 

 pressure, as heavy winds in 

 summer, although when exces- 

 sive weight is borne by sucli a 

 column the sides are liable to 

 collapse. To meet the former 

 condition, the stems of cereals 

 are hollow, while in the latter 

 case the stalk of corn has a 

 light filler. The cells of the 

 pith are very large and loosely 

 arranged, and although they do 

 not transport moisture, they do 

 act as reservoirs in time of 

 drought. During the final 

 stages of maiurity, after frost 

 has killed the leaves and the 

 stalk loses its color, the ker- 

 nels on the ear arc fed for some 

 The pith has one other func- 



Section of corn-stalk showing pith, flbro- 

 vascular bundles, and epidermis. 



time from the plant food stored here 



fioii, to hold in place the fibro-vasculav bundles. 



(4j The fibro-vascular bundles arc the circulatory ducts for the 



