THE ORGANIZATION OF THE INDIVIDUAL PLANT 135 



(seed leaves) in the seed, net-veined leaves, and flower parts usually in 

 fours or fives. They include a great many familiar plants. As examples, we 

 may cite such trees as oak, maple, sweet gum, apple, and orange; such 

 shrubs as oleander, lilac, wax myrtle, blackberry, blueberry, and gall- 

 berry; such vines as woodbine, grape, and poison ivy; and such herbs as 

 tomato, tobacco, carrot, bean, cabbage, clover, poppy, dog fennel, dan- 

 delion, thistle, and goldenrod. 1 Even this small number of examples is 

 sufficient to show how great a range in size, form, and growth habit exists 

 among the dicotyledons. Yet in spite of their superficial diversity, the 

 members of this group all share a basic structural and functional pattern 

 that we shall soon proceed to examine. 



COMPARISON OF PLANT AND ANIMAL ORGANIZATION 



Before entering upon our detailed study of the individual plant, it will 

 be well for us to look more closely at the principal similarities and differ- 

 ences between animals and plants. This will help our understanding of the 

 plant type of organization and some of its basic requirements, limitations, 

 and peculiar features. We shall see how the requirements of food manu- 

 facture account for all the most important features of plant structure 

 except those relating to reproduction. 



Features common to plants and animals. Like animals, plants are 

 made up of cells and cell products. The protoplasm of plant cells re- 

 sembles that of animal cells in appearance and properties and in nearly 

 all plants is similarly differentiated into nucleus (or nuclear material) 

 and cytoplasm. Each cell of the plant, like that of the animal, is bounded 

 externally by a living cell membrane. Unlike most animal cells, the cells 

 of plants are also usually enclosed in a more or less rigid, nonliving cell 

 wall secreted by the cell; this is not an essential difference, since some 

 plant cells are naked, whereas some animal cells, such as those of bone 

 and cartilage, are similarly enclosed by a nonliving cell product. The 

 cell wall of most plant cells is composed of cellulose, a substance chemically 



1 The flowering plants, or angiosperms, have two great subdivisions — the dicoty- 

 ledons, defined above, and the monocotyledons, the members of which have only one 

 seed leaf, parallel leaf veins, and flower parts usually in threes or multiples of three. 

 The grasses, palms, lilies, orchids, and many other familiar plants are monocotyledons. 

 The angiosperms are placed with the gymnosperms (pines, cycads, etc.) to form the 

 division Spermatophyta, or seed plants — the highest of the four plant divisions. None 

 of the remaining types of plant produces seeds; they form the three lower plant divi- 

 sions (Pteridophyta, or ferns and fern allies; Bryophyta, or liverworts and mosses; 

 and Thallophyta, or algae, fungi, lichens, bacteria, etc.). The members of these three 

 lower divisions are simpler in structure than the seed plants and differ more or less 

 markedly from the structural and functional pattern here described. Their features of 

 organization are briefly discussed in Chap. XIII, and a more detailed treatment of 

 plant classification will be found in Appendix A. 



