A SIX-STAMENED FLOWER IN ZEA MAYS L.

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1 130 A SIX-STAMENED FLOWER IN ZEA MAYS L. BY B. C. Department of Botany, University of Leeds (With 2 figures in the text) During the examination of the tassel of a maize plant, a number of flowers were found with more than the usual three stamens. They fell into the following classes: (1) A number with two separate stamens plus two stamens with a joint filament, making four anthers in all. (2) A considerable number with four distinct stamens. (3) Some with three separate stamens plus two 'double' stamens, each made up of two anthers with a joint filament, making five anthers in all. (4) Some with four separate stamens plus two anthers with a joint filament, making six anthers in all. (5) A few with five separate stamens. (6) A single specimen with six separate stamens. This last seemed so interesting that it was decided to section it in order to obtain an insight into its morphology. The flower, which completely occupied a normally two-flowered spikelet, was fully open when found and showed two glumes, inside which were two more bracts, presumably lemmas. At right angles to the plane of the glumes and lemmas was a pair of membranous structures, which were followed by the six stamens, all six of which arose at the same level and obviously came off the same common tissue. The sections illustrated in Fig. i a-d show the relationship of the parts at different levels. Each figure is based on two or three sections in order to compress the stages into as few figures as possible. Fig. i a is taken just above the separation of the glumes and shows the next two bracts, marked Y' and Y", beginning to separate from the rachis: the one on the left will have three bundles, while that on the right is provided with four. In the periphery of the rachis will be seen four separate strands: a pair of which lead to each of the structures placed at right angles to the plane of the glumes and lemmas, and marked X' and X" in Fig. i c, d. The remaining vascular tissue, shown shaded in Fig. i a, is composed of two masses which higher up provide the strands for the six stamens and four lodicules, and even at the level of Fig. I a are beginning to be organized into separate patches. Fig. I c shows the way in which the six stamens are all inserted on the axis in a ring at the same level. A small piece of tissue, marked Z, appears in two sections (total height, 12 p). Other than this there is no suggestion of a continuation of the rachis; nor are there any central bundles which might run to any supposedly 'suppressed' parts. Fig. i d shows the appearance above the separation of the structures X' and X", the four lodicules and the six stamens. The bases of the filaments of two sets of two stamens will be seen to be still slightly fused at this level.

2 A six-stamened flower in Zea Mays L. 131 but immediately above this they are completely free. Fig. 2 a, for comparison, illustrates the relationship of the parts of the two flowers in a normal spikelet. Although the abnormal flower, as its internal structure shows, is deflnitely a single structure, it can perhaps best be considered morphologically as being the result of the coalescence" of two flowers ' fused back to back'. Normally the spikelets are two-flowered (Fig. 2 a), the spikelet axis ceasing growth early after the production of the second lateral floret^ bud and usually not being traceable above this level in the adult spikelet. This condition is illustrated diagrammatically in Fig. 2 d. G' Fig. I. Transverse sections through the six-stamened male flower oi Zea. G', G", glumes i and 2; Y', Y'\ lemmas i and 2; X', X", palea-like structures; a', V and a", h", vascular bundles for X' and X"; Lo, bundles for lodicules; Z, small mass of tissue only 12 ft high which perhaps may be regarded as being the continuation of the rachis; F, filaments of the six stamens. Occasionally the rachis apex continues actively longer than usual and three lemmas are produced, each having an axillary bud, giving rise to a three-flowered spikelet in the adult, a condition which is illustrated diagrammatically in Fig. 2 e. On the other hand, an early cessation of activity leads to the production of a single, pseudoterminal flower in the spikelet as figured by Malpighi (Arber, 1934) and represented diagrammatically in Fig. 2 b. fn the six-stamened flower described above, presumably the growth of the spikelet axis ceased rather earlier than usual, so that when the two axillary floret buds developed in the axils of the lemmas, they were ' The term 'floret*is used here and below to cover that which develops in the axil of the lemma, i.e. the flower proper (essential organs and perianth as represented by the lodicules) plus the palea or prophyll of the axis on which the flower is born. 9-2

132 B. C. SHARMAN free to occupy a more central position than usual, with the consequence that both grew up together as a single, massive, probably slightly indented, meristem.

3 132 B. C. SHARMAN free to occupy a more central position than usual, with the consequence that both grew up together as a single, massive, probably slightly indented, meristem. On this arose the two bracts X' and X", each perhaps being initiated from two points but growing up as a single unit by the rapid lateral spread of the initiation, leading to a complete absence of any doubleness in the appearance of the adult structure. Fig. 2 c is a diagrammatic illustration of this spikelet for comparison with the single, normal and three-flowered spikelets shown in Fig. 2,b, d and e respectively. This curious single-flowered spikelet parallels a similar phenomenon reported by Kempton (1913) and Stratton (1923) for the female inflorescence. In the cob the spikelets are also two-flowered; usually the lower one is aborted and only the Fig. 2. a. Diagrammatic transverse section of normal two-flowered male spikelet. b, d and e. Diagrammatic representations of single-flowered, normal two-flowered and three-flowered spikelets. c. Ditto of the flower and spikelet illustrated in Fig. i. G', G", glumes i and 2; L', L,", lemmas I and 2; P', P", paleas I and 2; Lo, lodicules; F, filaments; R, imaginary continuation of rachis; X', X" and Y', Y", parts which ai;e labelled similarly in Fig. i. upper one is fertile, though in certain strains (e.g. Country Gentleman) both may develop normally. In a strain grown by the Hopi Indians of Arizona and in a hybrid derived from varieties from China, Salvador and Mexico, Kempton observed what he termed 'connate' grains single large grains caused by the back-to-back fusion of two embryos and their endosperms, so that a germ appears on each side of the grain. He concludes that ' The development of two ovaries in one spikelet must be simultaneous, as a large number of cases have been found where the two seeds from one spikelet have grown together with a single pericarp', but his illustrations of the mature caryopses suggest that there never has been any actual 'fusion', but rather that the connate grains have arisen from single massive twoovuled ovaries..

4 A six-stamened flower in Zea Mays L Blaringhem (1920) described as Zea Mays var. polysperma a strain of maize in which many double grains developed. This variety was examined by Stratton (1923), who showed that the double kernels arose from coalesced flowers, in which both of the flowers of the spikelet were fertile and had developed from the time of their inception in various degrees of 'fusion'. Her figures leave little doubt that this was brought about by the early discontinuance of the spikelet axis, allowing the two laterally developing floret buds to occupy a more central position than usual, and thus grow up as a single two-ovuled unit. Thus the six-stamened male flower described above is to be regarded as a single flower, probably developed from a single massive apex formed from two lateral buds originating close to each other. Morphologically it can be regarded as being composed of two florets'coalesced back to back'. REFERENCES AREER, AGNES (1934). The Gramineae: a study of Cereal, Bamboo, and Grass. Cambridge. BLARINGHEM, L. (1920).' Production par traumatisme d*une forme nouvelle de mai's k caryopses multiples, Zea Mays var. polysperma. C.R. Acad. Sci., Paris, 170, 677. REMPTON, J. H. (1913). Floral abnormalities in maize. Bull. U.S. Bur. PL Ind. no STRATTON, MILDRED E. (1923). The morphology of the double kernel in Zea Mays var. polysperma. Mem. Cornell Agric. Exp. Sta. no. 69.

DEVELOPMENT OF THE INFLORESCENCE AND SPIKELETS OF ANTHOXANTHUM ODORATUM L.

DEVELOPMENT OF THE INFLORESCENCE AND SPIKELETS OF ANTHOXANTHUM ODORATUM L. BY B. C. SHARMAN Department of Botany, Bedford College, Regent's Park, London, N.W.i {Received 4 January 1959) (With Plates 3