Survey of Plant Kingdom 143 



ovule. A pollen tube is formed through which the male pollen grain 

 (sperm) may travel to reach the Qgg. In gymnosperms single fertilization 

 occurs in which one sperm is involved in fertilizing the egg. Gymno- 

 sperms are considered in greater detail in a later chapter. 



Examples: Pine tree (Pinus) (Figs. 52 and 53) and cycad or sago 

 palm (Zamia) (Fig. 54). 



Angiosperms. — The angiosperms, or flowering plants, which pro- 

 duce their seeds enclosed in an ovary (carpels) , belong to the class Angio- 

 spermae (an ji o -spur' me) (Gr. angios, enclosed; sperma, seed). 



The sporophyte is large and independent (when mature), while the 

 gametophyte is small and dependent (upon the sporophyte). Angio- 

 sperms possess true roots, stems, and leaves. A well-developed vascular 

 system is present. Two kinds of spores (heterospory) are produced; 

 namely, m,icros pores, which form male microgametophytes, and mega- 

 spores, which form female megagametophytes. Flowers of some kind are 

 characteristic. True seeds are enclosed in an ovary (carpels). 



Pollination occurs by wind, insects, or birds, rarely by water. A pollen 

 tube is formed, extending from the stigma of the pistil down through the 

 style to the ovary, where the male sperm unites with the egg (ovum) 

 (Fig, 71). In angiosperms double fertilization occurs in which one 

 sperm (male nucleus) fuses with the egg (true fertilization) to form a 

 zygote, which will form the multicellular embryo. The other sperm 

 (male nucleus) fuses with two polar nuclei in the female gametophyte 

 to form the nutritive, efidosperm tissue to be used by the developing 

 embryo. Angiospermous plants are considered in greater detail in a later 

 chapter. 



Characteristics of Dicotyledonous and Monocotyledonous Angiosperms 



DICOTYLEDONOUS ANGIOSPERMS 



Two embryonic seed leaves 



Flower parts usually in 4's or 5's or 



multiples of these 

 Leaves net-veined 



Some have woody stems, others have 

 herbaceous stems 



Vascular bundles of stems usually ar- 

 ranged in a circle (cylinder) 



Cambium (meristematic tissue) be- 

 tween the phloem and xylem of vas- 

 cular bundle 



Examples: Beans (Figs. 55 and 56), 

 sunflowers (Fig. 57), roses, violets, 

 clovers, snapdragons, potatoes, elms, 

 oaks, apples, maples, hickories, pop- 

 lars, lilacs, etc. 



MONOCOTYLEDONOUS ANGIOSPERMS 



One embryonic seed leaf 



Flower parts in 3's or multiples of 3 



Leaves parallel-veined, and usually 

 long and narrow 



Most have herbaceous stems (few ex- 

 ceptions) 



Vascular bundles scattered throughout 

 stem 



No cambium between the phloem and 

 xylem usually 



Examples: Corn (Figs. 58 to 60), 

 wheat, bluegrass, lilies, irises, daffo- 

 dils, cattails, etc. 



