342 PRINCIPLES OF NATURAL ARRANGEMENT. 



genera with, and others without these pellucid dots. The clear 

 or milky character of the juices of the leaves and stalks, indicat- 

 ing as it does the absence or presence of certain secretions which 

 are characteristic of particular orders, will often prove of much 

 use in distinguishing their members. At the base of the leaf- 

 stalks are often found little leafy appendages (which are in fact 

 leaves, in an imperfect state of development), termed Stipules ; 

 the presence or absence of these frequently enables the Botanist 

 to distinguish the plants of two allied orders, of which one pos- 

 sesses them, whilst the other does not ; and certain peculiarities 

 in them, which will be hereafter noticed, are occasionally very 

 characteristic of particular groups. 



496. Passing on to the Flowers, we first have to notice the 

 characters afforded by the bracts ; these are seldom of any use in 

 distinguishing orders, on account of their constant variation within 

 the limits of each; but they are often valuable in separating 

 genera and species. The calyx is used in a variety of ways to 

 distinguish orders ; but the characters it affords are far from 

 being of equal or uniform importance throughout. The number 

 of sepals is sometimes a very useful and constant mark of a par- 

 ticular order ; thus, in Cruciferae, the Cabbage and Turnip tribe, 

 they are always four, and in Papaveracese, 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 

 importance 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 (as in Fig. 127), 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, 



