28 INTRODUCTION. 
and Turnip tribe they are always four, and in Papaveracee, the Poppy 
tribe always two; but in many orders it is extremely variable. The 
equal or differing size of the sepals is another character of great im- 
portance in some cases, but not to be regarded in others. Again, the 
union of the sepals by the adhesion of their edges is a character to which 
great value may usually be attached; when this adhesion unites all the 
sepals, the calyx is commonly said to be monosepalous (single-sepalled ;) 
but the term gamosepalous, expressing the union or adhesion of the 
sepals is to be preferred. A still more important character is the degree 
of adhesion of the calyx to the organs it includes. Where it arises 
immediately from the disk or expanded top of the flower stalk, and 
where the corolla, stamens and pistil are quite distinct from it, arising 
by themselves from the disk, the calyx is said to be inferior to the ovary, 
or non-adherent to it. But where the calyx seems to spring from the 
top of the ovary or seed-vessel, instead of beneath it, it is called superior; 
this conformation is due to the adhesion of the calyx to the wall of the 
ovarium, so that it forms a tube completely enclosing it, as in the Rose, 
Apple, &c. In some plants the calyx is altogether absent; and then the 
general rule is that the corolla is likewise deficient. Such plants are 
said to be Achlamydeous, the essential parts of their flowers being 
destitute of envelope. In the Composite, however, which possesses 
a corolla, the calyx is present in an undeveloped form, constituting the 
down of pappus, which surrounds the bottom of the corolla, and is 
- 32. In regard to the number and regularit: - of the parts of the corolla, 
nearly the same may be said as of the calyx. These characters are 
valuable in some instances and not in others. The separation or 
adhesion of the petals, constituting what is commonly known as the 
polypetalous or monopetalous corolla is often a character of first-rate 
importance. Still, from the cause formerly mentioned, it is liable to 
some uncertainty, and ought not on that account therefore to be trusted 
too implicitly. Sometimes no corolla is to be found, the calyx still 
being present, and the plant is then said to be Avetalous (destitute of 
petals,) or Monochlamydeous (having but one envelope). This is a 
character, however, on which great reliance cannot be placed, since 
apetalous genera frequently present themselves, in orders which usually 
possess complete flowers,—an occurrence which is less common amongst 
monopetalous Exogens, than among those which have separate petals, 
so that the character is of more value in the former than in the latter. 
CHARACTERS OF NATURAL SYSTEM. 
33, When our attention is directed to the more essential parts of the 
flowering system,—the stamens and pistil,—we meet with some char- 
