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Show 130 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III. from the long-styled being quite smooth. Fritz Muller remarks that this difference between the pollen-grains of the two forms is evidently of service to the plant; for the grains from the projecting stamens of the shortstyled form, if smooth, would have been liable to be blown away by the wind, and would thus have been lost; but the little points on their surfaces cause them to cohere, and at the same time favour their adhesion to the hairy bodies of insects, which merely brush aO'ainst the anthers of these stamens whilst visiting the flowers. On the other hand, the s1nooth grains of the long-styled flowers are safely included within the tube of the corolla, so that they cannot be blown away, but are almost sure to adhere to the proboscis of an entering insect, which is necessarily pressed close against the enclosed anthers. It may be remembered that in the long-styled form of Linum perenne each separate stigma rotates on its own axis, when the flower is mature, so as to turn its papillose surface outwards. There can be no doubt that this movement, which is confined to the longsty led form, is effected in order that the proper surface of the stigma should receive pollen brought by insects from the other form. Now with Faramea, as Fritz Muller shows, it is the stamens which rotate on their axes in one of the two forms, namely, the shortsty led, in order that their pollen should be brushed off by insects and transported to the stigmas of the other form. In the long-styled flowers the anthers of the short enclosed stamens do not rotate on their axes, but dehisce on their inner sides, as is the common rule with the Rubiacero ; and this is the best position for the adherence of the pollen-grains to the proboscis of an entering insect. Fritz Muller therefore infers that as the plant became · heterostyled, and as the CHAP. III. RUBIACElE. 131 stamens of the short-sty led form increased in length, they gradually acquired the highly beneficial pow r of rotating on their own axes. But he has further shown, by the careful examination of many flowers, that this power has not as yet been perfected ; and, consequently, that a certain proportion of the pollen is rendered useless, namely, that from the anthers which do not rotate properly. It thus appears that the development of the plant has not as yet been completed; the stamens have indeed acquired their proper length, but not their full and perfect power of rotation.* The several points of difference in structure between the two forms of Fararnea are highly remarkable. Until within a recent period, if any one had been shown two plants which differed in a unifonn manner in the length of their stamens and pistils,-in the form of their stigmas,-in the manner of dehiscence and slightly in the size of their anthers,-ancl to an extraordinary degree in the diameter and structure of their pollen-grains, he would have declared it impossible that the two could have belonged to one and. the same species. SUTERIA (species unnamed in the herbarium at Kew) (RUBIACEJE ). I owe to the kindness of Fritz Muller dried flowers of thiR plant from St. Catharina, in Brazil. In the long-styled form the stigma stands in the mouth of the corolla, above tho antherR, * Fritz l\iiiller gives another instance of the want of absolute perfection in the flowers of another member of the Rubiaceoo, namely, Posoqueria fragrans, which is adapted in a most wonderful manner for cross· fertilisation by the &gency of moths. (See 'Bot. Zeitung,' 1866, No. 17.) In ac-cordance with the nocturnal habits of these jn ects, most of the flowers open only during the night; but some open iu the da,y, and the pollen of such flowers i:::~ robbed, ns Fritz Miiller has often s en, hy humble-bees and other in ects, without any b •nefit being thus conferred on the plant. K 2 |