ANGIOSPERM^E 



363 



The Floral Leaves 



The peculiar leaves making up the floral structures are, next to the 

 seeds, the most characteristic structures of the Angiosperrns. Be- 

 sides the sporophylls and perianth-leaves, we may include under 

 this head of floral leaves the showy bracts which occur in many 

 plants, surrounding the inflorescence and often performing the func- 

 tions of showy petals. Such are the Spathes of the Aracese, the 

 bracts of the showy Dogwood ( Cornus Jloridd), of many species of 

 Euphorbia, etc. 



The Root 



The root in the Angiosperms, like the 

 stem, never shows a single apical cell, but 

 the tissues at the apex form two or more 

 layers of primary meristem, showing some 

 variation in different cases. The branching 

 of the roots is always monopodial, and the 

 secondary roots arise from the pericycle, as 

 they do in the Gymnosperms. 



The primary root of the embryo may 

 persist as a tap-root (Radish, Dandelion, 

 etc.), or it may be replaced by secondary 

 lateral roots, a condition always found in 

 the Monocotyledons, and common in many 

 Dicotyledons. 



The modifications of roots are similar to 

 those of the stem. Roots may be enlarged 

 for purposes of storage, a condition found 

 in many plants useful as vegetables (Beet, 

 Turnip, Carrot, etc.). Aerial roots are devel- 

 oped, which serve for support, e.g. those 

 developed near the base of the stem in 

 Indian-corn, and the very much larger ones 

 of many tropical trees, .e.g. Screw-pines, FlG ^27. Raceme of 

 Banyan, Mangrove, etc. Aerial roots also 

 serve for tendrils, e.g. Ivy, Poison-ivy 

 (R/ms toxicodendron) , etc., and in some epiphytic Orchids 

 and Araceee they absorb moisture from the air. 



Structure of the Flower 



Lily-of-the-valley. 

 (After BAILEY.) 





The more primitive types of flowers have all the parts separate, 

 and may be reduced to little more than a single carpel or stamen. 

 The floral envelopes may be entirely absent (Peperomia, Saururus), 

 but there are usually rudiments, at least, of a perianth. 



