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Show 148 HETEROSTYLED TRIMORPHIC PLANTS. CHAP. IV. capsules) was accidentally left during seve:al d~ys pressing against the net, and bees were seen ~nserting their proboscides through the meshes, and In consequence numerous capsules were forme~ on this one s1nall branch. From these several facts It follows that in sects will generally carry the pollen ~f each form from the stamens to the pistil of corresponding length ; and we shall presently see the importance of this adaptation. It must not, however, be supposed that the bees do not o-et more or less dusted all over with the several kinds ob f pollen; for this could be seen to occur w'ith the green pollen from the longest stamens. Moreover a case will presently be given of a long-styled plant producing an abundance of capsules, though growing quite by itself, and the flo':ers must have been fertilised by their own two kinds of pollen ; but these capsules contained a very poor average of seed. Hence insects, and chiefly bees, act both as general carriers of pollen, and as special carriers of t~e right sort. Wirtgen remarks* on the variability of this plant in the branching of the stem, in the length of the bractem, size of the petals, and in several other charact.ers. The plants which grew· in 1ny garden had theu l~aves, which differed much in shape, arranged oppositely, alternately, or in whorls of three. In this latter case the stems were hexagonal ; those of the other p~ants being quadrangular. But we are concerned c~1efly, with the reproductive organs: the upward bending of the pistil is variable, and especially in. the short-st!led form in which it is sometimes straight, sometimes sligh' tly curved, but generally b e~t. at n·g h t an gles~ The stigma of the long-styled pistil frequently ha * 'Verhand. des naturhist. Vereins, fiir Pr. Rhein!.' 5. Jahrgang, 1848, pp. 11, 13. CHAP. IV. LYTHRUM SALICARIA. 149 longer papilloo or is rougher than that of the 1ni 1- styled, and the latter than that of tho short-styl d; but this character, though :fixed and uniform in the two forms of Primula veris, &c., is her variabl , for I have seen mid-styled stigmas rougher than those of the long-styled.* The degree to which the longest and mid-length stamens are graduated in length and have their ends upturned is variable; so1neti1nes all are equally long. The colour of the green pollen in the longest stamens is variable, being som times palo greenish-yellow; in one short-styled plant it was almost white. The grains vary a little in size: I examined one short-styled plant with the grains above the average size; and I have seen a long-styl d plant with the grains from the mid-length and shortest anther· of the same size. We here see great variability in many important characters; and if any of these variations were of service to the plant, or were correlated with useful functional differences, the species is in that state in which natural selection might readily do much for its modification .. On the Power of Mutual Fertilisation between the three Forms. Nothing shows more clearly the extraordinary complexity of the reproductive system of this plant, than the necessity of making eighteen distinct unions in order to ascertain the relative fertilising power of the * The plants which I observed grew in my garden, and probably varied rather more than those growing in a state of nature. H. Muller has described the stigmas of all three forms with great care, and he appears to have found the stigmatic papillre differing co~lstantly in leugtiL and structure ~n the three forms, being longe::lt m the long-styled form. |
