378 



PART IV. VEGETABLE TAXONOMY. 



one-half, one third, one-fourth, though occasionally in a more 

 complex manner ; they are less commonly provided with stipules 

 than the leaves of Dicotyledons ; they are not usually articulated 

 to the stem, and the blades seldom branch into compound forms. 

 The flowers are most commonly constructed on the numerical 

 plan of three, and normally consist of five alternating whorls, 

 one of sepals, one of petals, two of stamens and one of pistils. 

 See Fig. 575, A. But there are numerous cases where one or 

 more entire whorls, or parts of some of them, have become 

 aborted, and in some instances, on the other hand, the number 

 is multiplied beyond the normal. In the Grasses, the outer whorl 

 of the perianth is entirely wanting, and the inner is usually only 

 partially represented by two small scales, one whorl of stamens 

 is usually absent, and frequently but one or two of the carpellary 

 leaves is present. See Diagram, Fig. 



575, C. 



In the Flowering-rush (Butomus), 

 on the other hand, all the whorls are 

 present, the outer staminal one con- 

 tains six instead of three stamens, 

 and there are two whorls of three 

 carpellary leaves each, composing 

 the gynaecium. See Fig. 576. In 

 the majority of cases, the perianth 

 whorls, when present, are similar in 

 color, as in the Tulip and Iris, but 

 sometimes the calyx is green and the corolla colored, as in 

 Trillium and Tradescantia. 



The seeds, in most cases, possess a copious endosperm, with 

 a relatively small embryo, but in some species, as most Orchid- 

 acese, no endosperm is formed at all; and in the Alismacese, 

 Naiadacea? and Juncagineae, it is formed, but very soon disap- 

 pears ; and in the Scitaminea a copious perisperm is developed 

 in its stead. 



But perhaps the most distinctive characteristic of the group 

 lies in the structure of the embryo. This is monocotyledonous ; 

 that is, instead of an opposite pair of cotyledons, as in many 

 Gymnosperms, and nearly all Dicotyledons, only one embryonic 

 leaf occurs on the first node ; if others are present, they alternate 



Fig. 576. — Diagram of flower of 

 Butomus. or Flowering-rush, show- 

 ing a doubling in the outer whorl of 

 stamens, and two whorls, instead of 

 one, of pistils. 



