104 NATURE OF PROSTRATE STEMS 



to the fact that certain nodes form roots and buds that develop 

 into new plants. In some cases, stolons, only the terminal bud 

 develops in this way and with the dying off of the old stem a 

 new plant is established, as in the houseleek (Fig. 70). In other 

 cases, runners, almost any node may form buds and roots which 

 become separate plants by the decay of the old stem, as in 

 the strawberry, gill-over-the-ground, cinquefoil, etc. These new 

 plants repeat the mode of growth of the parent plant and in 



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Fig. 70. Houseleek forming buds at the end of short branches or stolons. 



this way many prostrate stems spread out over the soil, estab- 

 lishing new plants in wider and wider circles. If you will ob- 

 serve the number of new plants established and the distances 

 traversed by some of these creeping stems each year you will 

 see the reason for the common occurrence of the large mats and 

 colonies of plants with prostrate stems. 



48. The Rhizome Type of Stems. — In a third type, the stems 

 have become so modified that they respond to the various stimuli 

 in quite a different way from the forms noted above. They 

 creep along in the soil and frequently resemble roots more than 

 stems. For this reason they are called rootstocks or rhizomes. 

 They are however, real stems, as is attested by the numerous 

 leaves and often erect branches that spring from their nodes 

 as seen in the ferns, sweet flag, cat tail, grasses, etc. Plants of 

 this type are well protected against drought and fires, and like 

 prostrate stems they are adapted to establishing new plants as 

 is apparent in grassy meadows, colonies of golden-rod and daisies 

 or reedy banks of cat tails, sedges, etc. These stems are also 

 well adapted to propagating new plants because they generally 

 serve as storage organs for food and are therefore often of a 

 fleshy character (Fig. 71). For these reasons it is sometimes 



a 



