Angiospermous Plants — Flowering Plants 207 



gonium. The three antipodal cells are regarded as remnants of the 

 prothallus tissue. A sex cell contains the N number of chromosomes. 



9. The adult sporophyte is large and independent, while the gameto- 

 phyte is very small and dependent (without chlorophyll) . 



10. Pollination occurs by pollen landing on the stigma and a pollen 

 tube being formed through the stigma, style, and part of the ovary. 



11. Water is not required for the fertilization of the ^g^ by the sperm. 



12. Pollination may be by wind, insects, birds (rarely by water), de- 

 pending upon the species. 



13. A so-called double fertilization occurs, in which one sperm (IN) 

 fuses with the egg (IN) (true fertilization) to form a zygote, with its 

 diploid (2N) number of chromosomes, which will develop into the 

 embryo. The other sperm (male gamete) fuses with the two polar nu- 

 clei in the center of the female gametophyte (megagametophyte), thus 

 forming a nucleus with the unique, triploid (3N) number of chromo- 

 somes. This triploid nucleus is called the primary endosperm nucleus 

 because its gives rise to the nutritive, endosperm tissue. The tube nu- 

 cleus usually disintegrates. 



14. The vascular (conducting) system of angiosperms typically con- 

 sists of long, tubular vessels composed of segments derived originally 

 from single cells which have been fused at maturity into long, continu- 

 ous tubes. In contrast, the conducting tissues of the xylem of gymno- 

 sperms are composed of single-celled tracheids. 



15. In the evolution of plants, from the simplest algae to the angio- 

 sperms, there has been an increase in the size and independence of the 

 sporophyte, while there has been a reduction in size and independence in 

 the gametophyte. 



16. The Angiospermae are divided into the subclasses (1) Dicotyledo- 

 neae (di kot i le -do' ne e) (Gr. di, two; kotyledon, embryonic seed leaf) 

 and (2) Monocotyledoneae (mon o kot i le -do' ne e) (Gr. mono, one; 

 kotyledon, embryonic seed leaf), which may be differentiated as follows: 



DICOTYLEDONEAE 



MONOCOTYLEDONEAE 



2 cotyledons (embryonic seed leaves) 



Net-veined leaves 



Vascular bundles of the stems usually arranged in 



a circle (cylinder) 

 Cambium (meristematic tissue) between the 



phloem and xylem of the vascular bundle 

 Some have woody stems; others have herbaceous 



stems 

 Flower parts usually in fours or fives, or multiples 



of these 



1 cotyledon 

 Parallel-veined leaves 

 Vascular bundles scattered 



throughout the stem 

 Usually no cambium 

 Mostly herbaceous stems 



(few exceptions) 

 Flower parts typically in 



three's or multiples of 



three. 



