252 MONOCOTYLEDONS. 



But there are other trilliums which differ greatly from this one. 

 The purple trillium (T. erectum) shown in fig'. 324 is very dif- 

 ferent from it. So are a number of others. But the purple 

 trillium is a species. It is made up of individuals variable, yet 

 very like one another, more so than any one of them is like the 

 white wake-robin. 



487. Genus. — Yet if we study all parts of the plant, the per- 

 ennial root stock, the annual shoot, and the parts of the flower, 

 we find a great resemblance. In this respect we find that there 

 are several species which possess the same general characters. 

 In other words, there is a relationship between these different 

 species, a relationship which includes more than the individuals 

 of one kind. It includes several kinds. Obviously, then, this 

 is a relationship with broader limits, and of a higher grade, 

 than that of the individuals of a species. The grade next higher 

 than species we call genus. Trillium, then, is a genus. Briefly 

 the characters of the genus trillium are as follows. 



488. Genus trillium. — Perianth of six parts : sepals 3, her- 

 baceous, persistent ; petals colored. Stamens 6 (in two whorls), 

 anthers opening inward. Ovary 3-loculed, 3-6-angled ; stig- 

 mas 3, slender, spreading. Herbs « ith a stout perennial root- 

 stock with fleshy scale-like leaves, from which the low annual 

 shoot arises bearing a terminal flower, and 3 large netted-veined 

 leaves in a whorl. 



Note. — In speaking of the genus the present usage is to say 

 trillium, but two words are usually employed in speaking of the 

 species, as Trillium grandiflorum, T. erectum, etc. 



489. Genus erythronium. — The yellow adder-tongue, or 

 dog-tooth violet (Erythronium aniericanum), sho\\ n in fig. 325, 

 is quite different from any species of trillium. It differs more 

 from any of the species of trillium than they do from each other. 

 The perianth is of six ])arts, light yellow, often spotted near the 

 base. Stamens are 6. The ovary is obovate, tapering at the 

 base, 3-valved, seeds rather numerous, and the style is elongated. 

 The flower stem, or scape, arises from a scaly bulb deep in the 

 soil, and is sheathed by two elliptical-lanceolate, mottled leaves, 



