SUNFLOWER LEAF 77 



5. No general bundle- sheath is present, though each bundle 

 is surrounded by a layer of colourless cells, without intercellular 

 spaces, which may be regarded as representing the bundle- 

 sheath. 



B. LAMINA. 



I. Take a piece of the lamina of the leaf of the Sunflower, 

 including the apex : it is important that it should be previously 

 bleached by treatment with alcohol : warm it gently in a mix- 

 ture of dilute glycerine and potash, and mount in glycerine : 

 examine with a low power, and observe 



1. The midrib, with its strongly marked vascular bundle, 

 running up to the apex of the leaf, where it terminates abruptly 

 in a mass of glandular tissue. 



2. Lateral branch-bundles the ribs or nerves passing off 

 from it, and forming a network by frequent anastomoses, while 

 some of them run up into and terminate in the serrate projec- 

 tions of the margin of the lamina. 



3. Smaller branch-bundles sometimes showing blind endings 

 in the parenchyma which fills the meshes of the network. 



II. Cut off a small square piece of the lamina of a leaf of 

 HelianthuSy including one of the main ribs or nerves, and 

 embed in paraffin (see directions, p. 9), so that the rib shall 

 be perpendicular. Cut transverse sections, and mount in 

 glycerine. 



Good sections may be obtained even from fresh material by 

 holding the piece of lamina between slices of carrot, or pith ; or 

 by folding the whole lamina repeatedly, and cutting sections 

 from the whole mass. 



Note with a low power 



1. The general outline of the section, which is irregular and 

 undulating, though it is in the main of uniform breadth. At the 

 point corresponding to the main nerve the section widens out, 

 the nerve appearing semilunar, as in the petiole. The convex 

 side is the inferior (adaxial or dorsal), and the concave the 

 superior abaxial or ventral) surface. 



2. That the margins of the sections (i.e. the superior and 



