234 - Multicellular Plants 



growing point (Fig. 12-38), from the peri- 

 cycle, a layer of meristem tissue that sur- 

 rounds the core of the root. Accordingly, 

 each new secondary root must break its way 

 out through the cortical tissues of the old 

 root. Some plants can form adventitious 

 roots from the meristem tissue in any part of 

 the stem, and in rare cases, even from leaf 

 meristem. 



Flowers develop at the ends of special 

 stems, which are unable to grow beyond a 

 fixed limit. Initially a floral bud looks much 

 like a foliage bud, but later the terminal 

 leaves modify their development and become 

 the sepals, petals, stamens, and carpels. In 

 the case of mixed buds, both foliage and 

 floral branches originate from the same bud. 



Vegetative Methods of Reproduction. 

 Many plants exhibit a variety of reproduc- 

 tive processes that do not involve the pro- 

 duction of either gametes or spores. In these 

 vegetative methods of reproduction, the new 

 plant usually arises from some multicellular 

 part of the parent that contains some meri- 

 stem tissue. 



Many liverworts and ferns, and a few seed 

 plants, form modified lauds, called bulbils or 

 gemmae, which develop into new plants alter 

 they become detached from the parent. Other 

 plants — such as the strawberry — send out 

 runners, or prostrate stems, producing off- 

 spring from the buds of the runners. New 



plants may also arise from the buds, or eyes, 

 of swollen underground stems, called tubers 

 (for example, the potato). Bulbs, which are 

 swollen underground buds, produce new 

 btdbs in the axils of the scalelike leaves; and 

 each new bulb can give rise to a separate 

 plant. 



In many plants, a slip, or cutting — that is, 

 a piece cut from a stem — may send out ad- 

 ventitious roots and develop into a new 

 plant; and in a few cases, a leaf, or even a 

 portion of a leaf, may do the same thing. 

 Grafting, on the other hand, involves the 

 combining of portions of two plants, and 

 grafting has become a valuable and widely 

 practiced technique among fruitgrowers (Fig. 

 12-39). All vegetative methods of propagation 

 provide a practical advantage to nurserymen. 

 Vegetative reproduction never involves the 

 processes of meiosis and fertilization, and 

 therefore the new plant always (barring mu- 

 tation) receives exactly the same set of chro- 

 mosomes and hereditary characters as was 

 possessed by the parent plant. Accordingly, 

 the nurseryman is sure that the desirable 

 qualities ol a certain fruit tree, or potato, 

 or other commercially valuable species are 

 perpetuated in the new plants. A number of 

 seed plants, including the banana, have lost 

 their capacity for forming functional seeds, 

 and are propagated solely by vegetative 

 methods. 



TEST QUESTIONS 



1. Make labeled sketches showing the main fea- 

 tures of: (a) the sporophyte; and (b) the 



gametophyte, of a fern. 



2. What is the basis lor recognizing the leafy 

 fern plant as a sporophyte, and the prothal- 

 lium as a gametophyte? 



3. Specify five major groups in the plant king- 

 dom and explain how the representatives of 

 each group arc to he distinguished on the 

 basis of their life cycles. 



4. A. Make labeled sketches to show the main 

 stages in the life cycles ol: (a) Spirogym, and 

 (b) the bread mold: 



B. Indicate the haploid and diploid slages 



and specify the points where meiosis and fer- 

 tilization occur. 



5. Identify each of the following structures and 

 give their localization in either the moss, or 

 the fern, or both: (a) sporangia: (b) sporo- 

 cvtes: (c) spores: (d) sorus; (e) antheridia: 

 (f) archegonia: (g) venter; (h) rhizoids: (i) 

 fertilized egg; (j) foot: (k) protonema: (1) api- 

 cal notch. 



6. Describe the life cycle of Selaginclla. Why is 

 this cycle generally considered to represent a 

 transition between the cycles of the ferns and 

 seed plants? 



7. Identify and locate each ol the following 



