The long-styled pistil is to that of the short-styled as 100 to 36 in length; and its divergent stigmas are longer by fully one-third of their own length than those of the short-styled form. In the latter the anthers are a little larger, and the pollen-grains are as 100 to 80 in diameter, compared with those from the long-styled form.

Cinchona micrantha (Rubiaceae).

Dried specimens of both forms of this plant were sent me from Kew. (3/26. My attention was called to this plant by a drawing copied from Howard's 'Quinologia' Table 3 given by Mr. Markham in his 'Travels in Peru' page 539.) In the long-styled form the apex of the stigma stands just beneath the bases of the hairy lobes of the corolla; whilst the summits of the anthers are seated about halfway down the tube. The pistil is in length as 100 to 38 to that of the short-styled form. In the latter the anthers occupy the same position as the stigma of the other form, and they are considerably longer than those of the long-styled form. As the summit of the stigma in the short-styled form stands beneath the bases of the anthers, which are seated halfway down the corolla, the style has been extremely shortened in this form, its length to that of the long- styled being, in the specimens examined, only as 5.3 to 100! The stigma, also, in the short-styled form is very much shorter than that in the long-styled, in the ratio of 57 to 100. The pollen grains from the short-styled flowers, after having been soaked in water, were rather larger--in about the ratio of 100 to 91--than those from the long-styled flowers, and they were more triangular, with the angles more prominent. As all the grains from the short-styled flowers were thus characterised, and as they had been left in water for three days, I am convinced that this difference in shape in the two sets of grains cannot be accounted for by unequal distension with water.

Besides the several Rubiaceous genera already mentioned, Fritz Muller informs me that two or three species of Psychotria and Rudgea eriantha, natives of St. Catharina, in Brazil, are heterostyled, as is Manettia bicolor. I may add that I formerly fertilised with their own pollen several flowers on a plant of this latter species in my hothouse, but they did not set a single fruit. From Wight and Arnott's description, there seems to be little doubt that Knoxia in India is heterostyled; and Asa Gray is convinced that this is the case with Diodia and Spermacoce in the United States. Lastly, from Mr. W.W. Bailey's description, it appears that the Mexican Bouvardia leiantha is heterostyled. (3/27. 'Bulletin of the Torrey Bot. Club' 1876 page 106.)]

Altogether we now know of 17 heterostyled genera in the great family of the Rubiaceae; though more information is necessary with respect to some of them, more especially those mentioned in the last paragraph, before we can feel absolutely safe. In the 'Genera Plantarum,' by Bentham and Hooker, the Rubiaceae are divided into 25 tribes, containing 337 genera; and it deserves notice that the genera now known to be heterostyled are not grouped in one or two of these tribes, but are distributed in no less than eight of them. From this fact we may infer that most of the genera have acquired their heterostyled structure independently of one another; that is, they have not inherited this structure from some one or even two or three progenitors in common. It further deserves notice that in the homostyled genera, as I am informed by Professor Asa Gray, the stamens are either exserted or are included within the tube of the corolla, in a nearly constant manner; so that this character, which is not even of specific value in the heterostyled species, is often of generic value in other members of the family.

CHAPTER IV.

HETEROSTYLED TRIMORPHIC PLANTS.

Lythrum salicaria. Description of the three forms. Their power and complex manner of fertilising one another. Eighteen different unions possible. Mid-styled form eminently feminine in nature. Lythrum Graefferi likewise trimorphic. L.

The Different Forms of Flowers on Plants of the Same Species Page 60

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Charles Darwin

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