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MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



degree of environmental control. A noteworthy 

 and extensive study of growth and development 

 under essentially natural environments was con- 

 ducted by Clausen, Keck, and Hiesey (4-) in Cali- 

 fornia. These investigators established transplant 

 stations along a transect running at the same 

 latitude from the coastal valleys to the high 

 Sierras. Clonally propagated plant material was 

 established at each station so that environmental 

 effect could be measured on the same genotype. 

 Photographs of typical response at each station 

 depict marked alterations in size, form, and de- 

 velopment. The primary transplant stations were 

 at elevations of 30, 1,400 and 3,050 meters. Tem- 

 perature differences were, of course, but one of 

 the major environmental variables. However, this 

 work depicts morphogenetic response of vegeta- 

 tion to an array of climatic conditions, many 

 being typical of extended range areas in the 

 southwestern United States, and serves to dem- 

 onstrate admirably the magnitude of plant mor- 

 phogenesis-environmental interaction. 



Let us now consider some examples of response 

 directly associated with temperature as the major 

 variable. Fischer (7) produced variations of leaf 

 shape in Ranunculus hirtus DC. by temperature 

 treatment. At 10° C. the leaves developed three 

 separate leaflets, while at 20° they were shallowly 

 lobed, with thinner and larger laminae subtended 

 by longer petioles. Taylor and McCall (35) found 

 in winter and spring wheat that length of cole- 

 optiles was increased by soil temperatures of 20° 

 to 24° C.j compared with cooler conditions of 

 12° to 16° C. Tillering was greater in the varie- 

 ties grown at the cooler temperatures, being 

 greatest when the soil was maintained at 16° C. 



In grasses, the form of the plant is affected 

 by the number and point of origin of tillers. 

 Ryle (28) examined tillering in seven perennial 

 grasses when grown overwinter in an unheated 

 glasshouse, compared with plants in a glasshouse 

 maintained at a minimum temperature of 15° C. 

 By relating tillering to the number of available 

 leaf axil sites, judged by the number of leaves 

 produced on the main shoot, he found that the 

 cooler environment enhanced tillering. A greater 

 proportion of tillers developed from the lower 

 axillary bud sites in the unheated glasshouse. 

 Species differed in number and leaf axil position 

 of their tillers. For example, S48 timothy pro- 



duced fewer tillers particularly at the lower nodes 

 than did the other species he studied. 



Separate control of soil and air temperatures 

 permitted Ketellapper (11) to grow Phalaris 

 tuberosa L. at a constant air temperature of 20° 

 or 30° C. with soil temperature being held at 20° 

 or 30° C. In regrowth following clipping, he ob- 

 served reduced tiller numbers with soil at 30° C. 

 under both air temperatures. Again coolness is 

 associated with greater tillering. Since the basal 

 nodes and tiller buds of grasses may be at or 

 slightly below the soil surface, soil temperatures 

 would be directly involved. 



Temperature is a consideration in practically 

 all ecological and physiological research, but 

 often its influence on conditions and processes 

 has not been translated into precise effects on 

 growth and development. We recognize that bio- 

 chemical change precedes visible morphological 

 change, but the sequence of events is seldom 

 known. Schwabe (29) reviewed morphogenetic 

 responses to climate and concluded that we have 

 a morphogenetic jigsaw puzzle for which we have 

 too few pieces to reveal an outline. Schwabe 

 enumerated substances involved in morphogenetic 

 control as including the nucleotides, enzymes, 

 hormones and inhibitors, and substrate mass, and 

 he envisions these as interacting simultaneously. 



Langridge (16) reviewed the literature partic- 

 ularly of temperature extremes affecting the 

 chemistry of growth processes in plants. The pre- 

 ponderance of this biochemical literature reports 

 research with bacteria. It has been found as tem- 

 peratures rise and growth ceases, that the addi- 

 tion of one or a few organic compounds will 

 often lead to growth resumption. Glutamic acid, 

 thiamin, and biotin have often been effective in 

 stimulating growth after high-temperature 

 growth cessation. Some investigators have re- 

 ported similar growth stimulation after thermal 

 inactivation in flowering plants, but the response 

 has not been as striking as with microorganisms. 

 Langridge discusses high temperature impair- 

 ment of growth from the standpoints of gas 

 availability (mainly C0 2 ), metabolite break- 

 down, temperature disruption or imbalance of 

 reaction rates, inhibition of enzyme formation, 

 and enzyme inactivation. 



The influence of supra-optimal temperatures 

 on nitrate reductase activity in young barley 



