. A textbook of botany for colleges and universities ... Botany. STEMS 727 Moisture as a factor in elongation. — Certain of the Crassulaceae (notably Sempervivum assimile, fig. 1043) usually are stemless in their natural xerophytic habitats, while growth in moist, light chambers results in the conspicuous development of erect leafy stems (fig. 1044); growth in moist, dark chambers results similarly, except that leaf formation is greatly reduced (fig. 1045). These and many similar experiments show conclusively that moisture favors elongation, while desiccation results in shortened and often in
. A textbook of botany for colleges and universities ... Botany. STEMS 727 Moisture as a factor in elongation. — Certain of the Crassulaceae (notably Sempervivum assimile, fig. 1043) usually are stemless in their natural xerophytic habitats, while growth in moist, light chambers results in the conspicuous development of erect leafy stems (fig. 1044); growth in moist, dark chambers results similarly, except that leaf formation is greatly reduced (fig. 1045). These and many similar experiments show conclusively that moisture favors elongation, while desiccation results in shortened and often in laterally enlarged stems; as might be expected,. Fig. 1046. — A potato plant (Solanum tuberosum), grown from a tuber planted with one end in the soil, but with the larger portion in the air; note the short and stout aerial shoots, which contrast strikingly with the long and slender shoot which originated in the soil; note also the much larger leaves on the latter shoot. — Photograph by Fuller. the presence of soluble salts in the culture media produces the same effect as desiccation. There are few if any similarly conclusive experiments as to light, and it seems probable that moisture differences constitute the chief factors in determining the phenomena noted in the preceding para- graphs. Indeed, in some cases (as in Jussiaea and in the seedlings of Vicia Faba) there is greater elongation in illuminated than in dark cul- tures, if the moisture conditions are equal and favorable. Stem inter- nodes become shorter and thicker and the plant more bushy, if the ordi- nary supply of carbon dioxid is doubled or quadrupled, but in nature this factor is not likely to be important. Variations in the length of petioles,. 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 Coulter, John Merle, 1851-1928; Barnes, Charl
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