. A textbook of botany for colleges and universities ... Botany. REPRODUCTION AND DISPERSAL 843. in such a way that it is Ukely to come into contact with the stigmas.' Commonly pollen-gathering insects are relatively non-specialized (ex- cept in the case of bees), corresponding in general to the lack of speciali- zation in the flowers, iii which the pollen is so exposed that it may be taken readily by any insect that visits it. Nectaries and nectar. — Nectar-secreting flowers commonly are more specialized than are nectarless flowers, and the nectar-gathering insects are the most specialized of
. A textbook of botany for colleges and universities ... Botany. REPRODUCTION AND DISPERSAL 843. in such a way that it is Ukely to come into contact with the stigmas.' Commonly pollen-gathering insects are relatively non-specialized (ex- cept in the case of bees), corresponding in general to the lack of speciali- zation in the flowers, iii which the pollen is so exposed that it may be taken readily by any insect that visits it. Nectaries and nectar. — Nectar-secreting flowers commonly are more specialized than are nectarless flowers, and the nectar-gathering insects are the most specialized of pollinating insects. How- ever, there are many simple actinomor- phic flowers with exposed nectar (notably among the umbellifers) or with nectar but sKghtly concealed (as in the crucifers), which are frequented by flies and by other insects with short probosces. From these simple nectar-producing flowers there are grada- tions in the degree of concealment of nectar to the highly specialized and often zygomor- phic forms in which it is concealed at a considerable depth at the base of long co- rolla tubes or in elongated spurs (fig. 1171), where as a rule only the most specialized insects with long mouth parts can obtain it. In most cases it is difiicult or even impossible for insects getting the nectar nous and zygomorphic-From i^ . . Barnes (Part II). to avoid rubbing agamst anthers and stigmas, thus facilitating pollination. As a rule, the pollen in nectar- bearing flowers is not abundant, and in long-tubed, and zygomorphic flowers it commonly is concealed. Most arctic and alpine flowers and also most vernal flowers of temperate climates are comparatively simple in structure and have their nectar supply relatively ex- posed. On the other hand, many tropical flowers and a large number of estival flowers of temperate climates have more specialized structures, their nectar supply being hidden in spurs or at the base of long corolla tubes. With the former there may be associate
Size: 1286px × 1942px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
