SUNFLOWER. LEAF. 91 



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. 



Bifadal Type. 



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 mixture 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 parenchy- 

 matous tissue. 



2. Lateral branch-bundles passing off from it, and 

 forming a network by frequent anastomoses, while 

 some branches run up into and terminate in the serrate 

 projections of the margin of the lamina in a manner 

 similar to the midrib as above described. 



3. Smaller branch-bundles, which sometimes end 

 blindly in the parenchyma filling the meshes of the 

 network. 



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

 leaf of Heliantlius, including one of the main ribs 

 or nerves, and imbed in cocoa-butter or paraffin (cf. 

 directions, p. 4), so that the rib shall be perpen- 

 dicular. Cut transverse sections, and mount in 

 glycerine. If cocoa-butter has been used, it may be 

 dissolved off the sections with ether or chloroform. 



