. Plant life, considered with special references to form and function. Plant physiology. '94 PLANT the different stimuli have received different names, and those names indicate the nature of the stinudus. A idant or an organ is helioinipic when it reacts to the dire<tion of tlie ra\'s of light falling upon it ; geo/ropic, when it reacts to the force of gravity ; lliermnlropic, when it reacts to the presence of a warm body ; hvdro/ropic, when it reacts to the presence of a moist surface, etc. In each case the plants are said to react posiiivelv when the movement is toward tlie source
. Plant life, considered with special references to form and function. Plant physiology. '94 PLANT the different stimuli have received different names, and those names indicate the nature of the stinudus. A idant or an organ is helioinipic when it reacts to the dire<tion of tlie ra\'s of light falling upon it ; geo/ropic, when it reacts to the force of gravity ; lliermnlropic, when it reacts to the presence of a warm body ; hvdro/ropic, when it reacts to the presence of a moist surface, etc. In each case the plants are said to react posiiivelv when the movement is toward tlie source of the stiumlus ; ?iegaliveh\ when the movement is away from the stimulus ; iransverselv, when it is transverse to the direc- tion of the stimulus. These reactions are to a certain extent. 190.—Diagrams representing tlie transverse lieliutropism of leaves of the garden nasturtium {I'roptFoium). Potted plants were subjected successively to light strik- ing them in the direction shown by arrows. 'J^lie petioles curved so as to place the blades at right angles to tlie incident light.—.^fter Viichting. related to one another, and it will be con\enient, therelore, to consider the effect of each stimulus upon the two common forms of plant organs—namely, the radial (such as stems and roots) and the dorsiventral (such as leaves). ()rgans are sometimes physiologically dorsiventral, even thoiigli they p)0ssess a radial structure ; for example, some stems licha\-(* as dorsiventral organs, although they are perfectly radial in structure. 285. [a) Heliotropism.—Heliotropism is the state of a plant or organ when it is irritable to the dii-ection of light Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Barnes, Charles Reid, 1858-1910. New York, H. Holt & company
Size: 2142px × 1166px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., book, bookcentury1800, bookdecade1890, booksubjectplantphysiology
