HIGHER LAND PLANTS 



189 



CLASS ANGIOSPERMAE (Flowering Plants) 



Diagnosis: definite remains no older than Lower 

 Cretaceous but questionable forms back to Mid- to 

 Upper Triassic; the most abundant group of living 

 plants; habit and growth form various, trees, shrubs, 

 and herbs; herbs perennial, biennial, and annual; a 

 natural group of seed plants distinguished from the 

 somewhat artificial group of gymnosperms primarily 

 by reproductive structures; angiosperms are unique 

 in the possession of true flowers; in pollen being spe- 

 cialized for transportation by water and organisms as 

 well as by wind; by the pollen tube having to travel 

 through several parts of a central floral structure 

 (pistil) to reach the opening (micropyle) of the ovule; 

 by a process of double fertilization involving the for- 

 mation of a nutrititive tissue (endosperm), as well as 

 the zygote; by the ovules (and seeds) being formed 

 within "vessels" (modified leaves) instead of "naked" 

 (upon the surface); by gametophyte development 

 generally being much more abbreviated; by garnet o- 



phytes typically being smaller, simpler structured, 

 and without definite sex organs; by embryos being 

 nourished by endosperm; and by the seeds being en- 

 closed within fruits. Include two major groups. Sub- 

 class Dicotyledoneae (dicots) and Subclass Mono- 

 cotyledoneae (monocots) whose features are con- 

 trasted in Figure 1 1 .27. 



The "vessel" enclosing the ovule has nothing to do 

 with the veins, or xylem or phloem; rather it is part 

 of a structure called a carpel, which in turn is the 

 prime component of a pistil. A simple pistil is com- 

 posed of a stigma (pollen receiver), a style (a connect- 

 ing link), and an ovary (ovules, hence seeds, are 

 formed inside). A compound pistil is formed by fu- 

 sion of simple pistils into a single structure. Each 

 simple pistil, or unit of a compound pistil, is a carpel 

 (a modified female sporangium-bearing leaO. There- 

 fore, both ovules and young seeds are enclosed in the 

 ovary portion of a single carpel, so either the ovary or 

 entire carpel can be considered "the vessel." 



The fruits are the containers of mature seeds. Fruits 



Figure 11.27 Dicots (Subclass Dicotyledoneae) to the left contrasted with monocots (Subclass 

 Monocotyledoneae) to the right ot each pair of diagrams: A, net venation vs. parallel venation of 

 leaves; B, flower parts usually in fives (also twos and fours) vs. in threes (or multiples of three); C, 

 usually with taproots vs. with fibrous roots; D, vascular bundles in o single cyclinder (forming a growth 

 ring each year) vs. scattered (no cambium to form annual rings); E, embryo with two developmental 

 leaves vs. with one developmental leaf — (1) seed coat, (2) sporangium wall or nucellus, (3) endo- 

 sperm, and (4) embryo. (Modified from various sources.) 



