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Show 120 HETEROSTYLED DIMORPHIC PLANTS. CHAP. III. below the other, the uppermost just protruding from the throat of the corolla. In Phlox subulata alone he has "seen both long and short styles; and here the short-styled plant has (irrespective of this character) been described as a distinct species (P. nivalis, P. Hentzii), and is apt to have a pair of ovules in each cell, while the long-styled P. subulata rarely shows more than one."* Some dried flowers of both forms were sent me by him, and I received others from Kew, but I have failed to make out whether the species is heterostyled. In two flowers of nearly equal size, the pistil of the long-styled form was twice as long as that of the short-styled; but in other cases the difference was not nearly so great. The stigma of the long-styled pistil stands nearly in the throat of the corolla; whilst in the short-styled it is placed low down-sometimes very low down in the tube, for it varies greatly in position. The stigma is more papillose, and of greater length (in one instance in the ratio of 100 to 67), in the short-styled :flowers than in the long-styled. My son measured twenty pollen-grains from a short-styled flower, and nine from a long-styled, and the former were in diameter to the latter as 100 to 93; and this difference accords with the belief that the plant is heterostyled. But the grains from the short-styled varied much in diameter. He afterwards measured ten grains from a distinct long-styled flower, and ten from another plant of the same form, and these grains differed in diameter in the ratio of 100 to 90. The mean diameter of these two lots of twenty grains was to that of twelve grains from another short-styled flower as 100 to 75: here, then, the grains from the short-styled form were considerably smaller than those from the long-styled, which is the reverse of what occurred in the former instance, and of what is the general rule with heterostyled plants. The whole case is perplexing in the highest degree, and will not be understood until experiments are tried on living plants. The greater length, and more papillose condition of the stigma in the short-styled than in the long-styled flowers, looks as if the plant was heterostyled; for we know that with some species-for instance, Leucosmia and certain Rubiacere-the stigma is longer and more papillose in the short-styled form, though the reverse of this holds good in Gilia, a member of the same family with Phlox. The similar position of the anthers in the two forms is some- * 'Proc. American Acad. of Arts and Sciences,' June 14,1870, p. 248. CHAP. III. ERYTHROXYLUM. 121 what opposed to the present species being heterostyled · as is the great difference in the length of the pistil in several 's·h ort-styled flowers. But the extraordinary variability in diameter of the pollen-grains, and the fact that in one set of flowers the grains from the long-styled flowers were larger than those from the short-styled, is strongly opposed to the belief that Phl()x subulata is heterostyled. Possibly this species was once heterostyled, but is now becoming sub-dioocious; the short-styled plants having been rendered more feminine in nature. This would account for their ovaries usually containing more ovules, and for the variable condition of their pollen-grains. Whether the long-styled plants are now changing their nature, as would appear to be the case from the variability of their pollen-grains, and are becoming more masculine, I will not pretend to conjecture; they might remain as hermaphrodites, for the coexistence of hermaphrodite and female plants of the same species is by no means a rare event. ERYTHROXYLUM [SP. ?] (ERYTHROXYLID.B!l). Fritz Muller sent me from South Brazil dried flowers of this tree, together with the accompanying drawings, which show the two forms, magnified about five times, with the petals removed. Fig. 8. Long-styled form. Short-sty led form. From a sketch by Fritz Muller, magnified five times. ERY'l'HROXYL0:8 [sp. ?]. |