198 PRACTICAL BOTANY 



cell has grown out as a conical papilla : it is these 

 which give the velvet-like appearance to the corolla : 

 the mesophyll which is very lax, and is not differentiated 

 into palisade and spongy parenchyma. 



Sections should also be cut of the sepals and petals 

 of other flowers, such as the Pansy, Pelargonium, Scilla, 

 &c., in order to compare their structure with that of 

 foliage leaves. 



The bright colours of flowers and fruits may be due 

 either to colouring matter dissolved in the cell-sap, or 

 to small coloured bodies in the cells, or to both com- 

 bined. They must be studied in fresh material, as the 

 colourings are altered or destroyed by alcohol. As a 

 first example the common scarlet Geranium (Pelar- 

 gonium) may be taken, in which the petals owe their 

 colour to dissolved matter. 



Strip off the superficial tissue from a petal of this 

 plant, and mount in water with the outer surface 

 uppermost : note under a low power the conical form 

 of the superficial cells, and the bright red colour of 

 the cell-sap : chromoplasts or formed granules appear 

 to be entirely absent. 



The case of the common red and yellow Tulip is a 

 good example of mixed colouring : strip off the super- 

 ficial tissue from the yellow base of one of the segments 

 of the perianth : mount in water, and examine under 

 a high power : observe the very numerous yellow 

 chromoplasts of more or less distinctly crystalline form. 



Strip off now a similar patch of tissue from the 

 upper, red portion, mount, and examine as before : here 

 the chromoplasts will be seen as before, but masked 

 by the more prominently coloured red cell-sap. 



