MONOCOTYLEDONS 423 



underground stem is in the form of a solid, scaly bulb from 

 which two characteristically spotted leaves and a single flower 

 scape grow each spring. The most distinctive feature of Erythro- 

 nium is the peculiar method by which the bulbs of each season 

 become more deeply buried in the soil. The new bulbs are 

 formed at the ends of runners arising from buds in the axils of 

 the scale leaves. The runners of each season (Fig. 269) grow 

 downward and so bury each new daughter bulb a little deeper in 

 the soil than the mother bulb. Six or seven years are necessary 

 for the production of a bulb strong enough to bear flowers. The 

 seasonal history of Erythronium and Smilacina is therefore not 

 unlike that of the tulip and hyacinth or of a perennial woody 

 plant in which a long period of vegetative activity is necessary 

 before reproduction by flowers and fruit is possible. 



Reproduction. The flowers in Smilacina and Erythronium differ 

 from those of Tradescantia in that both whorls of the perianth 

 are colored like a corolla and are therefore not differentiated 

 into a distinct calyx and corolla. This feature is also character- 

 istic of the cultivated lilies, tulips, and hyacinths, to which 

 Smilacina and Erythronium are closely related. Cross-pollination 

 is effected by insects, since the stamens, when ripe, are shorter 

 than the pistil, so that the stigma protrudes beyond the anthers. 

 It is thus in a position to receive pollen from insects which 

 have recently visited other flowers. 



The fruit in Smilacina (Fig. 267, C) is a berry, and the seeds 

 are disseminated when the berry disintegrates, or they may be 

 distributed by animals which eat the fruit. In Erythronium the 

 fruit is a capsule which splits into three valves corresponding 

 to the three carpels of the ovary, thus disseminating the seeds. 



IRIDACEAE AND ARACEAE (!RIS AND ARUM FAMILIES) 



The species of these two families are of particular interest on 

 account of the special adaptations of the flowers for securing 

 cross-pollination by insects. Their vegetative characteristics are 

 also of biological importance as indicating the characteristic habit 

 of the aerial and underground parts of the monocotyledons 

 already emphasized in Tradescantia and Liliaceae. 



