ii6 PRACTICAL BOTANY 



Cut transverse sections of the same, mount in glycerine, and 

 observe that the structure is altogether simpler than that of 

 the foliage leaf. Note the smooth lower epidermis : the upper 

 epidermis, of which each 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. 



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 combined. They must be studied 

 in fresh material, as the colourings are altered or destroyed by 

 alcohol. As a first example the common scarlet Geranium 

 (Pelargonium] 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 superficial 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 chromo- 

 plasts will be seen as before, but masked by the more 

 prominently coloured red cell-sap. 



THE STAMEN. 



III. All the following preparations should be made from 

 materials hardened in alcohol, or fixed with saturated solution 

 of picric acid, and then washed, and hardened in alcohol. 



A. Cut transverse sections of a flower bud of Caltha palustris, 

 which was just ready to open, taking care that the anthers shall 

 be cut through transversely. Neglecting the other parts, mount 



