ao March, 191^- 



W//caf and its Cidiivatlon. 



In the higher plants the transference of water from cell to cell by 

 'Osmotic agencies alone would be far too slow to keep ])ace with the water 

 '.requirements of the leaves. Specially developed structures are therefore 

 found in these plants, and serve as conducting media whereby the water 

 taken in at the root finds its way rapidly to the leaf. Fig. 10 shows a 

 ■cross section of a young root of Federation wheat. Several delicate root 

 hairs {r.h.) will be observed, each forming simply an elongated cell of the 

 •epidermis. In the centre of the root is the axillary vascular bundle ((u.b.) 

 which runs throughout the length of the root and ultimately merges Into 

 -similar structures in the stem. 



Fig. 15 is a longitudinal section through one of the vascular bundles 

 •of the stem. 



Each bundle consists, mainly, of a series of elongated cells with ligni- 

 fied thickened cell walls, and a variety of long cylindrical vessels forming 

 -continuous open tubes, with and without spiral thickenings. These ves.sels 

 originally contained protoplasm, 

 but during the course of growth 

 the protoplasm was used for 

 thickening the cell walls, and the 

 matured vessels are merely long 

 tubes specially adapted for con- 

 ducting water. 



The dilute solution of mineral 

 plant food, which has diffused 

 through the root hair, epidermis, 

 and root tissue, now finds its wa\ 

 to the conducting tissues of thf 

 axillary vascular bundle, and is 

 conveyed through similar tissues in 

 the stem to the leaf. 



^. 



LONGITUDINAL SECTION OF YOUNG 

 WHEAT ROOT SHOWING AXILLARY 

 VASCULAR BUNDLE {v.h.) FOR 

 CONDUCTING SAP, ALSO ROOT 

 HAIRS ir.h.). 



Structure and Function of 

 THE Leaf. 



What takes place when the 

 dilute mineral solution reaches the 

 leaf may best be understood by 

 referring to the structure of the 

 wheat blade. Fig. 16 is a 

 transverse section of a leaf of Federation wheat. Above and below, 

 the leaf is bounded by a single layer of epidermal cells, and lying 

 between is the mes^phyll. The upper portion of the mesophyll is typicalh 

 closer in structure than the lower portion, which is usually spongy in 

 character and contains a large number of intercellular spaces. These 

 intercellular spaces form labyrinthic chambers in which air freely circulates 

 in the interior of the leaf. Scattered through the body of the mesophyll 

 are the vascular bundles which form in wheat a set of parallel strands 

 serving not only as a skeleton for the support of the remaining leaf tissue, 

 but also as media for the conduction of the sap to every part of the leaf. 

 The cells of the mesophyll contain a large number of green bodies called 

 chloroplasts or chlorophyll corpuscles, which give the leaf its characteristic 

 green colour. The epidermis (Fig. 17) of the leaf in contrast to that 

 of the root is studded with microscopic openings called stomata, more or 

 less regularly placed. Each stoma or pore consists of two sausage-shaped 



