THE FLORAL ENVELOPES. 135 



Sometimes, by the mere juxtaposition of the different cells 

 in the petals, a mechanical admixture of their various contents 

 takes place ; thus is probably produced that delicate and inimi- 

 table shading seen in the petals of some flowers; at other 

 times, the petals are spotted and variegated, as in the tiger 

 lily and balsam. Such spots result from the peculiar power, 

 possessed by some of the cells, of attracting from the colorless 

 sap these particular colors, and of which power the other cells 

 appear to be deprived. No admixture of color with the neigh- 

 boring cells takes place in this case. "In the petals of 

 Impatiens balsamina, the garden balsam," says Dr. Lindley, 

 " a single cell is frequently red in the midst of others that are 

 colorless. Examine the red bladder, and you will find it filled 

 with a coloring matter of which the rest are destitute." 



Every one must have noticed the regularity with which 

 these spots are formed in the petals of certain flowers, which 

 are in fact never without them. Such cells appear to have 

 definite functions assigned them, the exercise of which is pro- 

 bably as important to the healthy vital action of the plant as 

 that of the most elaborate organs. 



The chromule, or coloring substance of plants, is by no 

 means confined to their petals, but sometimes pervades the 

 sepals of the calyx, as we have already shown, and is even 

 occasionally extended into the tissue of the bracts and ordinary 

 leaves of the stem. The beautiful wild flower called Castilleja 

 euchroma, or the painted cup, owes all its beauty to its con- 

 spicuous and deep scarlet bracts; and in Croton pictum, a 

 plant which may be frequently met with in conservatories, the 

 chromule tints the ordinary leaves of the plant. The analogy 

 of the petals to the leaf is thus clearly traceable ; and how- 



