MONOCOTYLEDONS 425 



The cultivated forms of Iris have a similar habit and also 

 a similar floral structure, which has become highly modified by 

 hybridization and selection with a view to increasing the size, 

 color, and beauty of the flowers. 



Reproduction. The flower (Fig. 270, A) is epigynous, with the 

 floral parts arranged in sets of three each. The outer lobes of 

 the perianth are large and highly colored, while the inner ones 

 are smaller and less conspicuous. The three stamens spring from 

 the base of the outer perianth lobes, and each stamen is beneath 

 a branch of the three-lobed style. The stigmas are on the upper 

 surface of a flap which grows out from each stylar lobe. When 

 an insect visits the flower for nectar, it comes to rest upon one 

 of the outer lobes of the perianth and then crawls down into the 

 flower to probe for nectar at the base of the perianth. In so doing 

 it dusts pollen onto its back, which cannot reach the stigmatic 

 surface as it crawls out, but is in a position to pollinate a stigma 

 of the next flower visited. The pollen germinates quickly on the 

 stigma of Iris, and. the pollen tubes follow down the stylar canal 

 in the center of the style to the ovules, where fertilization takes 

 place. The flower is thus admirably adapted to cross-pollination 

 by insects. 



ARACEAE (ARUM FAMILY) 



AEISAEMA (JACK-IN-THE-PULPIT) 



Habitat and habit. The common jack-in-the-pulpit (Arisaema 

 triphyllum) is one of the most familiar representatives of the Arum 

 family in the spring flora. It grows naturally in moist humus soil 

 in the shade of trees and is thus mesophytic in habit and habitat. 



The aerial stem bears one or two leaves and peculiar greenish 

 flowers. The underground stem is a turnip-shaped corm which 

 bears the annual aerial shoot from a terminal bud. 



The seasonal history of the jack is an interesting one and will 

 serve as another illustration of the peculiar adaptations of some 

 of the monocotyledons with underground stems for perpetuat- 

 ing themselves by vegetative reproduction. The new roots arise 

 each year from the upper part of the corm (Fig. 271, A), while 



