96 THE WHEAT PLANT 



which are reduced in diameter : the finer strands pass into the hypodermal 

 stereome ring of the stem, or close to it, the larger ones arranging them- 

 selves nearer the centre in the pith of the straw. 



Of the 30 bundles in the leaf-sheath illustrated in I., Fig. 75, 13 

 (Nos. i, 3, 5, 7, 10, 12, 14, 16, 18, 20, 23, 27, and 29) go through the 

 node into the hypodermal stereome of the stem or near it (VI., Fig. 75), 

 the remaining larger strands (17) going into the pith. 



The small unnumbered hypodermal bundles seen in the section of 

 the stem (VI., Fig. 75) arise within the stereome of the leaf-sheath bundles 

 a short distance above the node (x, Fig. 75). 



In the internodes of the stem the bundles run longitudinally in parallel 

 lines ; traced downwards, they are found to enter the solid node. Just 

 below the point of junction of the leaf-sheath the fine hypoderm bundles 

 curve outwards, some of them at the same time spreading more or less 

 horizontally and uniting with each other to form a narrow more or less 

 broken ring (r, II., Fig. 75). A little lower the stouter, inner, larger 

 cauline bundles bend outwards and insinuate themselves between the 

 large leaf- traces, at the same time bifurcating or fusing with each other in 

 an irregular manner, some of the strands twisting and curling through the 

 central pith in various directions, others passing out into the cortical 

 parenchyma on the outer margin of the zone of large bundles. 



The 37 " pith " bundles of the stem (I., Fig. 75) found above the 

 node are reduced by fusion and anastomosis within the node to 16, 

 which are seen (not numbered) in the section of the stem below the 

 node (VI., Fig. 75), alternating more or less regularly with the 17 large 

 bundles which have come from the leaf-sheath. 



Generally in a section of an internode of a straw all the fine bundles 

 in the hypoderm and a few small bundles near it come from the leaf- 

 sheath immediately above ; of the larger bundles within the pith, about 

 one half come from the leaf-sheath, the other half descending through 

 the node from the internode above. 



In a transverse section the bundles in the leaf-sheath appear of the 

 ordinary collateral type with girders of stereome connecting them with 

 the outer epidermis (2, Fig. 57). Very near the base of the sheath, 

 however, the stereome strands are free from the epidermis, each becoming 

 oval in section (i, Fig. 57) : imbedded within them are the rudiments 

 of minute bundles (usually one but sometimes two in each) the first traces 

 of which consist of two or three leptome cells. 



On entering the node the stereome strand is reduced and finally 

 disappears : the minute bundle within the latter becomes more clearly 

 defined and can be traced through into the hypoderm of the stem below. 



As previously mentioned, some of the leaf-sheath bundles on entering 

 the node are reduced in size, but about half of them are greatly increased 



