SUNFLOWER LEAF 125 



by boiling for ten minutes in 10 per cent, solution of potash ; 

 then by means of forceps, and a stiff camel's-hair brush, the super- 

 ficial tissues and mesophyll may be removed, leaving the vascular 

 tissue as a continuous network, limited at the periphery by a 

 larger marginal bundle : mount the skeleton thus prepared on a 

 slide, and examine under low power : note especially (1) the 

 branchings and fusions of the ribs or nerves ; (2) the blind 

 endings of the smaller ones ; (3) the large peripheral bundle ; 

 (4) cells of the mesophyll still adhering to the bundles of the 

 network, and partially filling up the interstices. 



Various other leaves may with advantage be treated in a similar 

 manner, or observations may be made upon leaves of poplar, &c., 

 of which the softer tissues have rotted by lying on damp soil, 

 while the vascular system remains as a skeleton showing often 

 with great perfection the arrangement of the vascular network. 



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

 leaf of Helianthus, including one of the main ribs or 

 nerves, and embed in paraffin (see directions, p. 11), 

 so that the rib shall be perpendicular. Cut transverse 

 sections, and mount in glycerine. If cocoa-butter has 

 been used, it may be dissolved off the sections with 

 ether or chloroform. 



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. In these cases, though the chlorophyll appears 

 of a better colour, the sections not having been treated with a 

 solvent (alcohol), still they will be infested with air-bubbles, which 

 may be partially removed by leaving the sections for some minutes 

 in water : they may be completely removed (though the chlorophyll 

 would be dissolved) by more prolonged treatment with alcohol. 

 Difficulty will often be found in obtaining good preparations of 

 the above : all the important points may be more easily observed 

 in the leaves to be described below. 



