126 HISTOLOGY OF ANGIOSPERM STEM, ROOT, ETC. 



internal structure of floral leaves is, 011 the whole, simpler 

 than that of foliage-leaves. 



Note that the epidermis-cells often have the outer wall 

 dome-like or conical, and marked by striations ; in some 

 cases (e.g. Pansy) the epidermis -cells of the petals are 

 produced into long finger-like processes, given the velvety 

 or satin-like appearance of the petal surface. The lateral 

 walls of the epidermis-cells are often very wavy, or have 

 ingrowths resembling those seen in the mesophy 11- cells of 

 a Pine leaf. 



160. Chromatopliores and Coloured Sap. Strip the 

 epidermis from the perianth-leaves and petals of various 

 flowers. Note that in green floral leaves the colour is 

 due to chloroplasts ; in white leaves the cells contain 

 colourless plastids (leucoplasts) and colourless cell-sap. 

 In most yellow flowers the colour is due to yellow 

 chromoplasts, chiefly in the epidermis, but sometimes 

 (e.g. Narcissus perianth-lobes) in the mesophyll-cells. In 

 a few cases, however, the yellow pigment is dissolved in 

 the cell-sap, e.g. Mullein. Blue, violet, and some red 

 colours are due to coloured sap, but some reds are due to 

 chromoplasts. 



Examine the flowers of Narcissus, Pansy, Tropaeolum, 

 Buttercup, red Rose, Poppy, Wallflower, Myosotis, Crocus, 

 etc. Investigate cases of mixed colouring, e.g. red and 

 yellow Tulips and Zinnias (some epidermis -cells with red 

 sap, others with yellow chromoplasts). In each case 

 mount in water or glycerine strips of tissue torn or shaved 

 from the floral leaves. 



161. Structure of Mature Anther. The flower of a 

 Lily or a Narcissus may be used with advantage for the 

 structure of the anther and the ovule, but various other 

 flowers that are available should be tried. 



For transverse sections of the mature but intact 

 anther it is necessary to use young flower-buds. In the 

 case of Narcissus cut across (a) flower-buds still enclosed 

 in the resting bulb, (b) young flowers that have been 

 carried up in spring but have not yet opened. Note the 



