MICROSCOPIC OBJECTS. 19 



Fig. 37. Petal of Geranium (Pelargonium), x 150. 



The drawing of this petal is something like fig. 48 in 

 general appearance; but when the two are carefully com- 

 pared, they will be found to be quite different in structure. 

 For instance, the rayed appearance in the cells of the Gera- 

 nium is caused by a multitude of minute folds or wrinkles 

 radiating from a common centre in each cell. But it is 

 mainly the central mamillse that give the fine velvety feel to the 

 petals of many flowers, such as the Geraniums, Pansies, &c. ; 

 while the rayed appearance in the cells of the testa of the 

 Vegetable-Ivory nut is caused by the irregular formation of 

 the secondary deposit. 



This petal is best mounted dry. 



Fig. 38. Petal of a Crimson-flowered Cactus (Epiphyllum) , 

 N. O. Cactacese, x 350. 



The colour- cells of this petal are rather large, and form a 

 wavy kind of structure. The colour of the petal is a deep 

 crimson. The petals seem to contain, amidst their surround- 

 ing tissue, a more than ordinarily large number of spiral- vas- 

 cular cells, which will be seen on referring to the drawing. 

 Many petals contain spiral- vascular cells, which generally run 

 through their entire length (see fig. 36). The best way to 

 mount this petal is simply to soak it in ether for a minute, 

 then to place it in sulphuric acid 1 part, water 2 parts, for a 

 minute or so, until the colour becomes strong, then to wash 

 and dry it, and to mount it in balsam as usual. 



