. Introduction to botany. Botany. 214 Introduction to Botany. Fig. 130. Seed pods of the Cottonwood just before breaking open. Reduced. where the hairs are an outgrowth from the base of the seed, the total weight of the seed and hairs is miUigrams; while in the seed pod the hairs are closely appressed against the seed, but after the pod breaks open the hairs begin to dry and bend downward and outward, and in so doing they assume the form of a parachute and spread the seeds apart at the same time, so that the slightest puff of wind car- ries them away. On a single tree the pods may be break
. Introduction to botany. Botany. 214 Introduction to Botany. Fig. 130. Seed pods of the Cottonwood just before breaking open. Reduced. where the hairs are an outgrowth from the base of the seed, the total weight of the seed and hairs is miUigrams; while in the seed pod the hairs are closely appressed against the seed, but after the pod breaks open the hairs begin to dry and bend downward and outward, and in so doing they assume the form of a parachute and spread the seeds apart at the same time, so that the slightest puff of wind car- ries them away. On a single tree the pods may be breaking open in succession and offering their seeds to the wind for a space of two months, so that the seeds are quite certain to be borne away by winds from all direc- tions. In strong winds, such seeds must be car- ried to very great dis- tances (Fig. 131). In the tumbleweeds another method has been devised for employing the wind in scattering the seeds. These plants have a rounded general contour; when the seeds have ripened, the whole plant dies and breaks off close to the ground, and is easily rolled by the. Fig. 131. On the left seed pods of Cottonwood breaking open and the hairs on the seeds beginning to spread apart and push the seeds out of the pods; on the right, a later stage, the seeds ready to be wafted away by the wind. 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 Stevens, William Chase, 1861-. Boston, D. C. Heath & Co.
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