. Outlines of plant life : with special reference to form and function . Botany. 280 OUTLINES OF PLANT LIFE. mally spherical by the proportion of the branches. Such plants are known as '' tumble weeds.'' Singly or aggregated in large bundles they are rolled over plains and prairies for long distances, shaking out their seeds as they go, or opening their fruits when moistened. Another adaptation for distribution by the wind is the small size of some seeds. Those of some orchids are so diminutive that it takes 500,000 to weigh I gram. Such minute seeds are readily blown long distances by the win
. Outlines of plant life : with special reference to form and function . Botany. 280 OUTLINES OF PLANT LIFE. mally spherical by the proportion of the branches. Such plants are known as '' tumble weeds.'' Singly or aggregated in large bundles they are rolled over plains and prairies for long distances, shaking out their seeds as they go, or opening their fruits when moistened. Another adaptation for distribution by the wind is the small size of some seeds. Those of some orchids are so diminutive that it takes 500,000 to weigh I gram. Such minute seeds are readily blown long distances by the wind. Relative light- ness is also secured by the construction of some seeds, which are surrounded by a voluminous coat contain- ing many large air spaces Fig. 242,—Seeds of an orchid \Vanda teres"), icl _ .„\ r>iitmTiwt>ic with cells of seed coat bladdery and filled with (."g- 242J. UUtgrOWmS air. These seeds are ejected from the capsule fmrn narts nf tVi/-iirf the air varies. Magnified 100 diam.—After Oi pericarp aiSO secure '^"°"- the same end. In such cases the fall of the fruit or seed through the air is so retarded that it may be carried laterally some distance by the wind. No seeds, however small, float long in quiet air, since buoy- ancy is derived only from air-containing tissues. A flattened form of the fruit or seed is very common, and this form is often exaggerated by the formation of wings, , of thin out- growths from the surface (fig. 243). The center of gravity in such cases is so placed that the plane of flattening will be. 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 : Henry Holt and Company
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectbotany, bookyear1900
