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Show 254 CONCLUDING REMARKS CHAP. VI. and often thicker than those on that of the shortstyled. For instance, the papillro on the long-styled stio-ma of Hottonia palustris are more than twice the le:gth of those in the other form. This holds good even in the case of Houstonia crerulea, in which the stigmas are much shorter and stouter in the longstyled than in the short-styled form, for the papillm on the former compared with those on the latter are as 100 to 58 in length. Tho length of the pistil in the long-sty led form of Lin~~m grandijlorum varies much, and the stig1natic papillco vary in a corresponding manner. From this fact . I inferred at first that in all cases the difference in length between the stigmatic papilloo in the two forms was one merely o£ correlated growth; but this can hardly be the true or general explanation, as the shorter stigmas of the long-styled form of Houstonia have the longer papillm. It is a more probable view that the papillm~ which render the stigma of the long-sty led form of . various species rough, serve to entangle effectually the largesized pollen-grains brought by insects from tho shortstyled form, thus ensuring its legitimate fertilisation. This view is supported by the fact that the pollengrains from the two forms of eight species in Table 34 hardly differ in diameter, and the papillm on their stigmas do not differ in length. The species which are at present positively or almost positively known to be heterostyled belong, as shown in the following table, to 38 genera, widely distributed throughout the world. These genera are included in fourteen Families, most of which are very distinct from one another, for they belong to nine of the several great Series, into which phanerogamic .plants have been divided by Benthttm and Hooker. CHAP. VI. ON HETEROSTYLED PLANTS. 255 TABLE 35. List of Genera includin.g Ileterostyled Species. DICOTYLEDONS. DICOTYLEDONS. Cratoxylon. Hypericinere. Mitchell a. Rnbiacem. Erythroxylum. Erythroxylem. Diodia. Sethia. " ·" Borrcria. Lin urn. Geraniacero. Spermacocc. " Oxalis. " " Primnla. Primulacere. Lythrum. Lythracere. Hottonia.. , Nesroa. " Androsace. Cinchona. Rubiacere. For. ythia. Oleac"e re. Bouvardia. " Menyanthes. Gentianacere. Manettia. " Lirnnanthemum. Hedyotis. " " Villar:;ia. Oldenlandia. " " Gilia. Polcmoniacero. Houstonia. " Cordia. Cordi em. Coccocypsel um. " Pul monaria. Boraginero. Lipostoma. " 1Egiphila. Verbenacere. Knoxia. " Polygonum. Polygonere. Faramea. " Thyme lea. Thymelere. Psycho tria. Rudgea. " MONOCOTYLEDONS. Suteria. " " Pontederia. Pontederiacere. In some of these fan1ilios the heterosty led condition must have been acquired at a very remote period. Thus the three closely allied genera, Menyanthes, Limnanthemum, anJ. Villarsia, inhabit respectively Europe, India, and South America. Heterostyled species of Hedyotis are found in the ten1perate regions of North and the tropical regions of South America. Trimorphic species of Oxalis live on both sides of the Cordillera in South America and at the Cape of Good Hope. In these and some other cases it is not probable that each species acquired its heterostyled structure in.dependently of its close allies. If they did not do so, the three closely connected genera of the Menyantheoo and the several trimorphic. species of Oxalis must have inherited their structure from a common progenitor. But an inunonse lapse of time will have been necessary in all such cases for tho modified descendants of a common progenitor to have |