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MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



roots and subsequent tillering from that por- 

 tion. Furthermore, excessive crown elevation ex- 

 poses plants to great damage from fire and 

 grazing. 



Russian wildrye (Elymus junceits Fisch.) ex- 

 hibits an interesting elevation of crowns in late 

 summer or fall. A vegetative shoot may be ele- 

 vated a few centimeters by elongation of a stolon- 

 like internode (27). This elevation exposes the 

 shoot apices and rudimentary inflorescences to 

 winter damage. However, close grazing in late 

 summer and fall prevents the elevation and in- 

 creases seed production. 



We have yet to develop appropriate manage- 

 ment practices to counter crown elevation, wheth- 

 er by seedlings or established plants. However, 

 crown elevation by established grasses might be 

 prevented or reduced by periodic burning, rotary 

 hoeing, rotary beating, trampling and grazing 

 by livestock, or other treatment. Both the fre- 

 quency and season of treatment would be im- 

 portant. Treatment to prevent tillering from 

 higher nodes and permit tillering from the lower 

 nodes of the crown should increase tolerance for 

 extreme weather conditions and minimize de- 

 cline in productivity when considered over a 

 number of years. The summer slump in rate of 

 growth, also, might be reduced by forcing tillers 

 to arise from greater depths in the soil. 



The Vegetative Shoots 



Rhizomes and stolons. — Nonphototropic branch- 

 ing at the base of a shoot produces stolons above 

 ground or rhizomes below ground. Rhizomes pro- 

 vide advantages over stolons with reference to 

 the elevation of root and shoot primordia. On the 

 other hand, stolons contribute assimilates for 

 their own growth more readily than rhizomes. 

 Any branch depends on the parent shoot until 

 it has mature leaves and adventitious roots (42). 

 The initiation of nonphototropic branches from 

 axillary buds appears identical to that of pho- 

 totropic branches (tillers). However, long days 

 of summer generally favor rhizome and stolon 

 growth, while tillers tend to arise in the spring 

 and fall (13). Stolons generally are continuous. 

 forming roots and tillers as they go. Rhizomes 

 may be continuous or terminal. In the terminal 

 type, the rhizome turns upward in the autumn 



to become phototropic. However, defoliation in 

 the summer can cause terminal rhizomes to turn 

 upward and produce aerial shoots (1). In the 

 truest sense, both stolons and rhizomes are vege- 

 tatively indeterminate. The transition from non- 

 phototropic to phototropic growth by a terminal 

 rhizome is, nevertheless, a continuation of growth 

 by a single shoot apex. 



Culmless vegetative shoots. — Phototropic vege- 

 tative shoots, also are of two types — culmless and 

 culmed (22). Turfgrasses have been defined as 

 perennial species capable of forming a dense 

 sod (1$). One other condition might be included; 

 namely, they should produce culmless vegetative 

 shoots. In culmless vegetative shoots, the persis- 

 tent basal position of shoot apices and leaf inter- 

 calary meristems provides protection for the 

 sources of further leaf expansion and of leaf re- 

 placement after defoliation. Culmless vegetative 

 shoots are well adapted to frequent mowing 

 and grazing. Leaf growth stops during unfavor- 

 able conditions; but cell division and expansion 

 resumes in both apical and intercalary meristems 

 upon the resumption of favorable conditions. 

 Consequently, dead leaf tips are common on 

 spring growth, and may be exhibited with any 

 new surge of growth when exserted portions of 

 immature leaves die back during a period of 

 unfavorable conditions. Succession of the shoot 

 apex to reproductive status, or death by any 

 cause, terminates culmless vegetative shoots. 

 Otherwise, they remain active and indeterminate 

 in producing leaf tissue. Consequently, they can- 

 not be called annual or biennial structures. 



Cvtlmied vegetative shoots. — By contrast, 

 culmed vegetative shoots are characteristically 

 annual structures, dying back to the base after 

 the season of growth. The culmed type is at first 

 culmless because internode elongation generally 

 is much delayed compared to leaf growth. Subse- 

 quently, internode elongation elevates the shoot 

 apex and leaf intercalary meristems as well. Cut- 

 ting below the rise of the shoot apex stops leaf 

 expansion and prevents leaf replacement except 

 by the slower process of tillering from axillary 

 buds of the crown. 



The degree and timing of shoot apex elevation 

 by culmed vegetative shoots affects resistance 

 (tolerance) to grazing (5. 6). and the leaf re- 

 placement potential after defoliation (21). Any 



