Seedling Morphology of some selected members of Commelinaceae and its bearing in taxonomic studies

Seedling morphology of eight species from four genera of the family Commelinaceae viz. Commelina appendiculata C.B. Clarke, C. benghalensis L., C. caroliniana Walter, C. paludosa Blume, Cyanotis axillaris (L.) D. Don ex Sweet, C. cristata (L.) D. Don, Murdannia nudiflora (L.) Brenan and Tradescantia spathacea Sw. are investigated using both light and scanning electron microscopy. The seedling morphological features explored include germination pattern, seed shape, surface and hilum, root system, cotyledon type, cotyledonary hyperphyll (apocole), cotyledonary hypophyll (cotyledonary sheath), hypocotyl, first leaf and subsequent leaves. All taxa studied had hypogeal and remote tubular cotyledons. However, differences in cotyledon structure (apocole, cotyledonary sheath), seed, hypocotyl, internodes, first leaf and subsequent leaves were observed. Variations of those characters were used to prepare an identification key for the investigated taxa. Commelina spp. and Murdannia nudiflora of the tribe Commelineae were found to differ from Cyanotis spp. and Tradescantia spathacea of tribe Tradescantieae in the petiolate first leaf with papillate margins on upper surface with 6-celled stomata and the glabrous epicotyl. The presence of an elongated cotyledonary sheath, long apocole and extended periblast region appear to be synapomorphies for Commelina spp. and T. spathacea. The affinity of the investigated taxa as revealed through multivariate analysis supports some of the relationships inferred by pollen morphology, floral morphology and DNA (rbc-L, 5S NTS, trnL-trnF) data stated by previous authors.

The reproductive biology of Hydrocharis morsus-ranae. II. Seed and seedling morphology

This study of seed and seedling morphology in the aquatic monocotyledon Hydrocharis morsus-ranae L. (Hydrocharitaceae) represents part of a continuing study of sexual reproduction in this species. Scanning electron microscope studies of the seeds showed them to have testas covered with hollow spiraliform tubercles. Germination occurs when the radicle and cotyledon of the embryo from the exalbuminous seed elongate, splitting the tuberculate testa. The buoyant embryo then rises to the surface with the first foliage leaves emerging from a highly modified cotyledonary sheath. This makes early growth in the seedling look strictly hypocotyledonary. Both the radicle and cotyledon discontinue growth by the two-leaf stage in the seedlings. The young seedlings undergo several growth phases. At first they look Lemna-like in habit and then, subsequently, very similar to germinating turions of the same species. Several methods are discussed to help distinguish between germinating turions and seedlings. During a subsequent field study of a H. morsus-ranae population, only two germinating seedlings were discovered. Several reasons for the absence of seedlings in this population are discussed.

La genèse du bulbe et son enfouissement chez les semis de Tulipa gesneriana

In tulip seedlings, a cluster of slightly chromophilic cells are formed at the bottom of a small cavity at the base of the cotyledonary sheath. During the first 5 weeks of seed hydration, the cells of this cluster divide and thus form the apical meristem. When the first leaf is initiated, a hollow diverticulum, the dropper, differentiates at the base of the cotyledon. It is located laterally with respect to the axis of the plantlet. The dropper is produced by the tissues of the cotyledonary sheath, and partly by those of the hypocotyl. The dropper buries itself vertically in the substrate, drawing down the apical meristem which is enclosed within its extremity. At this stage, statocyts are observed in the wall of the dropper. The first leaf develops into a typical starchy bulb scale. Thus the primordial bulb is formed when the growth of the dropper is terminated.

Morphological Development and Germination of Dwarf Spikerush (Eleocharis coloradoensis)

Dwarf spikerush [Eleocharis coloradoensis(Britt.) Gilly] is an aquatic plant that will displace waterweeds. It was studied to obtain information that will help to manage unwanted vegetation in natural aquatic situations. The morphology of seed and tubers was examined at the light- and scanning-electron microscope levels. Inflorescences were found to bear 3 to 12 florets that matured acropetally. The pericarp was made up largely of rows of annulated cells covered with a water-soluble, waxlike substance that leached away when stored in water at 4 to 6 C. The seed coat consisted of three layers. Each layer contained lipids, giving evidence that they were composed of cutin. When the seed germinated, the cotyledonary sheath emerged first, followed by the culms. Tubers formed and matured in about 30 days. The shoot apices of tubers each had two buds that were protected by five to seven overlapping membraneous leaf scales. When tubers sprouted the longest bud grew first. The second bud contained the culm meristem.

Ontogenetic Studies on the Juvenile Leaves of Phoenix dactylifera L

The ontogeny of seedling leaves or eophylls of Phoenix dactylifera was studied from foliar initiation to the stage of laminal maturation. During germination, the embryonal axis is carried deeper into the soil by the elongating cotyledonary sheath. As soon as the root and shoot apices become active the elongation stops. The first foliar organ produced by the shoot apex is a prophyll, a structure that has a sheath but no lamina. The second product of the shoot apex is the first eophyll, which is simple, lanceolate, plicate and devoid of haut. The plications arise by the process of schizogenous splitting of cells of the laminal meristem and not by differential growth or by 'invagination' as reported by earlier authors working on other palm genera. The eophyll differs from the adult leaf in the mode of splitting and in the number of plications produced. The adaxial splits occurring in the eophyll start from the epidermis and proceed inwards, whereas they are internal for the most part and leave a continuous sheet of tissue (haut) in the adult leaf. The first eophyll develops only one split on either side of the rachis-petiole axis on the adaxial side followed by a similar splitting on the abaxial side. This limits the number of plications to a minimum. Ontogeny of the vasculature of the eophyll is traced from early stages.