528 A TEXTBOOK OF BOTANY [Ch. XIII 



type of bundle seems unfavorable to branching, which is 

 infrequent as compared with Dicotyledons ; but its absence 

 is compensated by the great size of the leaves. The 

 perfection of this arrangement is reached in the Palms, 

 with their tall unbranched trunks bearing at the summit a 

 crown of gracefully compounded fronds (page 60). For 

 a similar reason the simple leaves are usually parallel- 

 veined and entire, instead of variously emarginate as in 

 Dicotyledons. Owing to lack of cambium the Monocotyle- 

 dons cannot increase indefinitely in diameter, except in 

 those kinds which have developed a sort of cortical cambium 

 which grows steadily outward and lays down new bundles 

 (page 128). Commonly the leaves have sheathing bases, 

 which often conceal the stem. Large primary roots are want- 

 ing, their place being taken by many small secondary ones. 

 The flowers, sometimes inconspicuous but commonly showy, 

 have typically 3 carpels, 6 stamens, 3 sepals, and 3 petals, 

 the two latter whorls being usually shaped and colored 

 alike, and hence included under the one name of perianth. 

 They are mostly pollinated by insects, and in fitness thereto 

 some of the forms exhibit the most remarkable adaptations 

 found in the plant kingdom. Besides, they possess, like the 

 Dicotyledons, remarkable specializations of structure which 

 seem to run far beyond any possible utility to the plant. 

 The fruits also are greatly varied in structure, though they 

 are mostly adapted to dissemination by various animals. 

 The comparative infrequency of wind pollination and dis- 

 semination in this group is of course correlated with their 

 usual occurrence in sheltered situations. 



Ecologically the Monocotyledons are mostly terrestrial 

 mesophytes, with preference for warm moist places. Phylo- 

 genetically their origin is obscure, though the evidence 

 suggests derivation from the Dicotyledons, next to be 

 considered; and some investigators derive them from the 

 group Ranales (page 546). On this view they represent an 

 early offshoot developed in adaptation to the aquatic condi- 



