. Lessons with plants. Suggestions for seeing and interpreting some of the common forms of vegetation. n,whether by bees, wind, man, or other means. 270. The simplest means by which cross-fertili-zation is enforced is by dichogamy, or the different CROSS-WJEBTILIZA TION 235 times of maturing of the organs of the same flower (150ffl). Certain simple movements or habits of the pistils or stamens are often associated with dichogamy. Fig. 226 is a flower of one of the wUd phloxes. The stigmas are seen to be three, but these are closed until the stig- matic surfaces are receptive, which commonly oc
. Lessons with plants. Suggestions for seeing and interpreting some of the common forms of vegetation. n,whether by bees, wind, man, or other means. 270. The simplest means by which cross-fertili-zation is enforced is by dichogamy, or the different CROSS-WJEBTILIZA TION 235 times of maturing of the organs of the same flower (150ffl). Certain simple movements or habits of the pistils or stamens are often associated with dichogamy. Fig. 226 is a flower of one of the wUd phloxes. The stigmas are seen to be three, but these are closed until the stig- matic surfaces are receptive, which commonly occurs after the pollen is discharged. A similar behavior may be detected in the blue-bells in Fig. 176. In the middle flower the style is merely club-shaped ; in the lowest flower, the style has opened to three branches, but the pig. 226. anthers are shrivelled. Inasmuch nichogamous flower of as the period of blooming of any plant usually extends over several days at least, the dichogamous flower is likely to receive pollen from various flowers which are borne either upon the same or another 270a. Pistils of dichogamous flowers may accidentally receivepollen from the same flower; but Darwin and others have foundthat pollen is often impotent, or sterile, upon the associated is, if pollen from the same and from another flower wereto fall upon a stigma, the foreign pollen is the more likely to befecund. Foreign pollen is commonly prepotent. If, however, nopollen is received from another flower, the stigma may accept thepollen from the associated anthers. 236 WESSONS WITH PLANTS 271. It is evident that if self-fertilization is sooften excluded, the plant must frequently dependupon extraneous agents for the transfer of pollenand the perpetuation of its kind. 272. If the pupil were to shake the staminatecatkins of the hazel, birch or walnut when theyare mature, he would be surprised at the showers ofpollen which are discharged; and if he shouldwatch the destinatio
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Keywords: ., bookauthorbai, bookcentury1900, bookdecade1900, booksubjectbotany
