222 A TEXT-BOOK OF BOTANY 
united, so that the calyx is a little cup or tube (Fig. 208). 
In any case, the calyx is useful in the bud condition of the 
flower in protecting the more delicate parts within. Some- 
times the sepals and the petals look so much alike that they 
are spoken of together as the perianth, as in the common 
lily (Fig. 274). Occasionally there is only one floral set 
outside the stamens; and it has become the custom to call 
it a calyx, assuming that the corolla is lacking. In still 
other cases, there are no floral members outside the sta- 
mens; and then the flower is said to be naked. 
133. Petals.—The attractiveness of flowers usually 
depends upon their petals, and hence their differences in 
Fic. 208.—Flower of tobacco: A, sympetalous corolla, calyx urn-like; B, tube of 
corolla cut open and showing attachment of stamens; C, the pistil, showing 
ovary, style, and stigma.—After STRASBURGER. 
color and form are things of common experience. In many 
flowers the petals are entirely distinct from one another 
and can be pulled off separately. In many other flowers, 
