PROBLEM 3. Hoiv Complex Plants 



accidentally cut off, or a crayfish or lob- 

 ster acquires a new claw. In plants it is 

 called vegetative reproductioji or vege- 

 tative propagation. Many of our food 

 and ornamental plants are propagated in 

 this way. The piece of stem or a leaf that 

 is used in propagation is called a slip or 

 a cutting. See Exercise 12. 



Sometimes new roots and branches 

 form from plants without their becom- 

 ing completely separated from the par- 

 ent plant. From the strawberry plant a 

 long stem known as a runner grows 

 along the ground. After the runner is 

 several inches long, it produces at its end 

 a short upright stem with leaves and 

 roots. Each plant holds hands, so to 

 speak, with its mother plant and in time 

 stretches out a hand to its daughter. In 

 the black raspberry a drooping twig or 

 layer takes root where it touches the 

 ground. This method of vegetative re- 

 production is called layering. 



Other examples of vegetative reproduc- 

 tion. There are still other plants that re- 

 produce vegetatively from stems but the 

 stems are not easily recognized as such. 

 The white potato mentioned above is 

 really a stem although it grows under- 

 ground and has no leaves. It is consid- 

 ered a stem because of the arrangement 

 of its tissues and because it has tiny buds. 

 These buds are commonly called "eyes." 

 The fleshy underground stem is known 

 as a tuber. When the tuber or a piece of 

 it is planted, the eyes sprout, and new 

 stems, leaves, and roots grow. 



Some stems, unlike the enlarged and 

 fleshy tuber, are very much shortened 

 and compressed. The leaves which ordi- 

 narily are found along the sides of a 

 stem are thus very close together. Such 



Reproduce 449 



a compressed stem with its closely 

 crowded fleshy leaves is known as a 

 bulb. Bulbs are usually planted in the fall. 

 During the winter and early spring, 

 roots grow from the base and a longer 

 stem with leaves farther apart grows 

 from the center. There is often a flower 

 or flowers at the end of the stem. From 

 buds in the old bulb, usually one or two 

 large new bulbs and several small bulbs 

 form. During the next season or some 

 later season new roots and shoots can 

 grow from them. This is another vegeta- 

 tive method of reproduction. 



Even some roots are used in propaga- 

 tion. Sweet potatoes are roots. Set one 

 end of a sweet potato in a jar of water 

 and set the jar in a window. Both roots 

 and shoots will grow from it. Even a leaf 

 or a part of a leaf from some plants, 

 when cut ofl" from the rest of the plant 

 and kept moist, will produce new stems, 

 leaves, and roots. African violets and 

 bryophyllum are good examples. 



(Optional) Variations in the story of 

 reproduction. We are now quite well 

 acquainted with the ordinary story of 

 reproduction in both plants and animals. 

 You may be interested in some of the 

 exceptions to the story. In quite a num- 

 ber of plants — the common dandelion 

 is one — the unfertilized t<g^ or some 

 other cell in the ovule begins to divide 

 just as a fertilized &^<g would. Divisions 

 continue until there is a good embryo in 

 the seed. This process is known as par- 

 thenogenesis and is similar to partheno- 

 genesis in animals (see page 424). 



Most of us have eaten seedless oranges, 

 grapes (raisins), and grapefruits; occa- 

 sionally we may have seen seedless toma- 

 toes, apples, or pears. It is probably safe 



