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Show 316 CLEISTOGAMIC FLOWERS. C_HAP. VIII. error, though only a small proportion of them do so. This appears to depend in some cases on their anthers not containing even a trace of pollen, but more generally on bees not visiting the flowers. I twice covered with a net a group of flowers, and 1narked with threads twelve of them which had not as yet expanded. This precaution is necessary, for though as a general rule the perfect flowers appear considerably before the cleistogamic ones, yet occasionally so1ne of the latter are produced early in the season, and their eapsules might readily be mistaken for those produced by the perfect flowers. Not one of the twelve marked perfect flowers yielded a capsule, whilst others under the net which had been artificially fertilised produced five capsules ; and these contained exactly the same average number of seeds as some capsules from flowers out£ide the net which had been fertilised by bees. I have repeatedly seen Bombu.s hortorum, lapidarius, and a third species, as well as hive-bees, sucking the flowers of this violet: I marked six which were thus visited, and four of them produced fine capsules ; the two others were gnawed off by some animal. I watched Bombus hortorum for some tin1e, and whenever it came to" a flower which did not stand in a convenient position to be sucked, it bit a hole through the spur-like nectary. Such ill-placed flowers would not yield any seed or leave descendants; and the plants bearing them would thus tend to be eliminated through natural selection. The seeds produced by the cleistogamic and perfect flowers do not differ in appearance or nu1nber. On two occasions I fertilised several perfect flowers with pollen from other individuals, and afterwards marked some cleistogamic flowers on the same plants ; and the result was that 14 capsules produced by the perfect CHAP. VIII. VIOLA. 317 flowers contained on an average 9 · 85 seeds; and 17 capsules from. the cleistogamic ones contained 9 · 64 seeds,-an amount of difference of no significance. It is remarkable how much more quickly the capsules from the cleistogamic flowers are developed than those from the perfect ones ; for instance, several perfect flowers were cross-fertilised on April 14th, 1863, and a month afterwards (May 15th) eight young cleistogamic flowers were marked with threads; and when the two sets of capsules thus produced were compared on June 3rd, there was scarcely any difference between them in size. Viola odorata (white-flowered, single, cultivated va~ iety).-The petals are represented by mere scales as In the last species; but differently from in the last all five stamens are provided with diminutive anthers: Small bundles of pollen-tubes were traced from the five anthers into the somewhat distant stigma. The capsules produced by these flowers bury themselves in the soil, if it be loose enough, and there mature themselves.* . Lecoq says that it is only these latter capsules which possess elastic valves; but I think this must be a misprint, as such valves would obviously be of no use to the buried capsules, but would serve to scat~er the s~eds of the sub-aerial ones, as in the other spec~es of VIola. It is remarkable that this pl t - cord t D 1 . an ' ac Ing. o e pino, t ~oes. not produce cleistogamic Howe~ m one part of Lrgurra, whilst the perfect flowers are. t ere .abundantly fertile; on the other hand cleistogamic flowers are produced by it near T . ' Anothe f t · . . ur1n. r ac Is worth giVIng as an instance of corre-pt Vauc~er says ('Hist. PLys. des p. a:fo~s ~Europe,: tom. iii. · 1844, l'k . ) at V. h~rta and collina S1e ee w11s e bur y tlJ e·u capsules.- a so Lecoq, '~eograph. Bot.' tom. v. 1856, p. 180. f 'Su!l' Opera, Ja Distribuzione de~ Sess1 nelle Piante' &c. 1867 p. 30. ' , ' |