. A textbook of botany for colleges and universities ... Botany. 73° ECOLOGY r1?1:'>-'*'\-]Crf^- -,' '-- --^- ^ The possible /actors.—While the exact factors determining elongation'in par- tially buried stems are not clearly known, it is significant that only those stems exhibit elongation which develop adventi- tious roots in the moist sand (fig. 1050). Some trees (as the red cedar) ordinarily are of low stature, while other trees (as the euca- lyptus) are very tall; the factors determining the potential height of the stem in various species are quite unknown. Increasing height probably is
. A textbook of botany for colleges and universities ... Botany. 73° ECOLOGY r1?1:'>-'*'\-]Crf^- -,' '-- --^- ^ The possible /actors.—While the exact factors determining elongation'in par- tially buried stems are not clearly known, it is significant that only those stems exhibit elongation which develop adventi- tious roots in the moist sand (fig. 1050). Some trees (as the red cedar) ordinarily are of low stature, while other trees (as the euca- lyptus) are very tall; the factors determining the potential height of the stem in various species are quite unknown. Increasing height probably is accompanied by accelerated tran- spiration, and an increasing root system makes possible increased absorption. It is likely, however, that the transpiration increase gradually exceeds the increase of available water, owing to the conjunction of increased transpiring surface, increased exposure to transpiration, and increased length of the conductive tract; ultimately the available water may be sufficient merely to make good the loss by transpiration, leaving no surplus for elongation. This condition, ultimately reached in all trees, may be reached much sooner in some species than in others, owing to peculiarities of structure and behavior. If this hypothesis is valid, stem elongation in dune sand may be explained by the fact that the absorptive system increases as fast as the transpiration is accelerated; the distance traversed by water in reaching the topmost organs remains essentially the same, since the adventitious roots keep pace in their de- velopment with the increasing elongation of the Fig. 1050. — The apical portion of a plant of the red-osier dogwood {Camus stolonifera) that has been almost buried by dune sand; note the adventitious roots (r) that have issued from the stem; the main shoot (m) has been killed, but one of the lateral shoots (n) still keeps above the sand; note that the scars {w) left by the fall- ing of the scales of the previous winter bu
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
