Evolution and adaptation . tyle (the stigma) and that of the stamens is exactlyreversed in the two forms. The corolla is also somewhatdifferently shaped in the two forms, and the expanded partof the tube above the stamens is larger in the long-styledthan in the short-styled form. Another difference is foundin the stigma, which is globular in the long-styled, anddepressed on its top in the short-styled, form. The papillae 1 Many of the facts as to the occurrence of these cases were known beforeDarwin worked on them; but very little had been ascertained in regard to thesexual relation between th
Evolution and adaptation . tyle (the stigma) and that of the stamens is exactlyreversed in the two forms. The corolla is also somewhatdifferently shaped in the two forms, and the expanded partof the tube above the stamens is larger in the long-styledthan in the short-styled form. Another difference is foundin the stigma, which is globular in the long-styled, anddepressed on its top in the short-styled, form. The papillae 1 Many of the facts as to the occurrence of these cases were known beforeDarwin worked on them; but very little had been ascertained in regard to thesexual relation between the dimorphic and trimorphic forms, and it was here thatDarwin obtained his most interesting results. 62 Evolution and Adaptation on the former are twice as long as those on the short-styledform. The most important difference is found in the size ofthe pollen grains. These are larger in the long-styled form,being in the two cases in the proportion of ioo to 67. Theshape of the grains is also different. Furthermore, the long-. FlG. 5. — A, long-styled, and B, short-styled, forms of Primula veris. C, D, E,the three forms of the trimorphic flower of Lythrum salicaria, with petalsand calyx removed on near side. (After Darwin.) styled form tends to flower before the other kind, but theshort-styled form produces more seeds. The ovules in thelong-styled form, even when unfertilized, are considerablylarger than those of the short-styled, and this, Darwin sug-gests, may be connected with the fact that fewer seeds areproduced, since there is less room for them. The important Origin of Different Kinds of Adaptations 363 point for our present consideration is that intermediate formsdo not exist, although there are fluctuating variations aboutthe two types. Moreover, the two kinds of flowers neverappear on the same plant. Darwin tried the effect of fertilizing the long-styled flowerswith the pollen from the same flower or from other long-styled flowers. Unions of this sort he calls illegiti
Size: 1598px × 1564px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublisherlondonmacmillancol
