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Show 334 CLEISTOGAMIC FLOWERS. CnAP. VIII. species of Leersia only two stamens are fully developed ? * The anthers shed their pollen on the stigma ; at least in one instance this was clearly the case, and by tearing open the anthers under water the grains were easily detached. ~owar~ls the apox of the anther the grains are arranged In a single row and lower down in two or three rows, so that they could be counted; and there were about 35 in each cell, or 70 in the whole anther; and this is an astonishingly sn1all number for an anemophilous plant. The grains have very delicate coats, are spherical and about 7cf0-0 of an inch ("0181 mm. ), whilst those of the perfect flowers are about 70~ 0 of an inch ("0254 mm.) in dia~eter. M. Duval-J ouve states that the panicles very rarely protrude from their sheaths, but that when this does happen the flowers expand and exhibit well-developed ovaries and stigmas, together with full-sized anthers containing apparently sound pollen ; nevertheless such flowers are invariably quite sterile. Schreiber had previously observed that if a panicle is only half protrude~, this half is sterile, whilst the still included half 1s fertile. Some plants which grew in a large tub of water in my green-house behaved on one occasion in a very different manner. They protruded two very large much-branched panicles;. but the florets ne:er opened, though these included fully developeJ stigmas, and stamens supported on long filaments with large anthers that dehisced properly. If those florets had opened for a short time unperceived by me and had then closed again, the empty anthers would have been left dangling outside. Nevertheless t~oy yielded on August 17th an abundance of fine npe seeds. Here then we have a near approach to the * Asa Gray, 'Manual of Bot. of United States,' 1856, P· 540. CnAP. VIII. LEERSIA. 335 single case as yet known* of this grass pr clucino- in a state of nature (in Germany) p rfect flow r whi h yielded a copious supply of fruit. S ds from th •lc i - togamic flowers were sent by me to Mr. 1Cott in Calcutta, who there cultivated the plants in various .. ways, but they never produced perfect flowers. In Europe Leersia oryzoides is the sole representative of its genus, and Duval-J ouve, after exa1nining several exotic species, found that it apparently is the sole one which bears cleistogamic . flow rs. It ranges from Persia to North A1nerica, and specimens from Pennsylvania resembled the European ones in their concealed manner of fructification. There can therefore be little doubt that this plant generally propagates itself throughout an i1nmense area by cl istogamic seeds, and that it can hardly ever be invigorated by cross-fertilisation. It resembles in this respect those plants which are now widely spread, though they increase solely by asexual generation.t Concluding Rernarks on Oleistogamic Flowers.-That these flowers owe their structure primarily to the arrested development of perfect ones, we may infer from such cases as that of the lower rudimentary petal in Viola being larger than the others, like the lower lip of the perfect flower,-from a vestige of a spur in the cleistogamic flowers of Impatiens,-from the ten stamens of Ononis being united into a tube,-and other such structures. The same inference may be drawn from the occurrence, in some instances, on the same plant of a series of gradations between the cleistogamic and perfect flowers. But that the former owe their origin wholly to arrested development is * Dr. Ascherson, 'Bot. Zeitung,' 1864, p. 350. t I have collected several such cases in my 'Variation under Domestication,' ch. xviii.-2nd edit. vol. ii. p. 153. |