OSMOPHORES,FLORAL FEATURES,AND SYSTEMATICS OF STANHOPEA (ORCHIDACEAE)

The floral fragrance glands (osmophores) of 18 species of Stanhopea and Sievekingia were examined through a series of developmental studies at light and electron microscope levels including late bud stages through postanthesis. Various characters were identified to be of potential systematic value and were recorded for each species. These characters included: texture of the osmophore surface, number of distinct cell layers comprising the osmophore, nature of lipid inclusions in osmophore cells, and presence or absence of plastoglobuli in osmophore amyloplasts. These characters were combined with traditional features of floral lip morphology for cladistic analysis. Sievekingia was the postulated outgroup. Stanhopea ecornuta showed the largest number of plesiomorphic characters. Stanhopea pulla, S. annulata, and S. Candida were only slightly more derived. Stanhopea anfracta, S. gibbosa, S. martiana, S. oculata, S. radiosa, S. ruckeri, S. saccata, S. shuttleworthii, S. tigrina, S. vasquezii, and S. wardii form a monophyletic group that can be recognized by a labellum with an articulated epichile and a bicornuate mesochile (or hypochile). Stanhopea tricornis may be a hybrid between a species of Sievekingia and Stanhopea.     

MEIOTIC IRREGULARITY IN SPECIES AND INTERSPECIFIC HYBRIDS OF PINUS

This paper describes a comparative analysis of meiotic conditions in 61 individual trees representing 21 species and 22 interspecific hybrid combinations of the genus Pinus. Material was collected during three successive growing seasons at the Eddy Arboretum of the Institute of Forest Genetics at Placerville, California. Meiotic irregularity occurred in all species and hybrids examined; mean irregularity frequencies of individual trees ranged from 0 to 47.2 percent. Abnormalities in chromosome movement and their consequences, (1) precocious disjunction associated with the occurrence of univalents and (2) the failure of chiasma terminalization leading to lagging chromosomes and to chromosome breakage and fragments, account for most of the observed irregularity. The same kinds of irregularity occur both in the species and in the hybrids, but they were considerably more frequent in certain of the hybrids than in the related species. These abnormalities in chromosome movement seem to be characteristic of Pinus and are attributed primarily to rrechanical difficulties which attend the large pine chromosomes in meiosis. The most spectacular meiotic irregularities were the characteristic bridge-fragment configurations considered to be the result of crossing-over in heterozygous paracentric inversions. Inversion bridges were observed in 59 of the 61 trees and were as frequent in the species as in the hybrids. They apparently do not result from interspecific differentiation in chromosome structure but from spontaneous intra-specific rearrangements. The literature and work now in progress provide increasing evidence that introgression has been an important factor in the evolution of pine populations. The cytological study of pine chromosomes has failed to produce qualitative evidence of introgression, but the quantitative measurement of meiotic irregularity may serve as a useful criterion for recognizing the results of past hybridization.     

FLORAL NECTARIES AND TRICHOMES IN RELATION TO POLLINATION IN SOME SPECIES OF THEOBROMA AND HERRANIA (STERCULIACEAE)

Floral surfaces of two Theobroma spp. and one species of the allied genus Herrania (Sterculiaceae) were examined using scanning electron microscopy for reward system information of the pollinator-adaptation syndrome. These flowers are structurally complex and have sheltered reproductive parts indicating an elaborate insect-mediated pollination mechanism. Analysis of anther dehiscence, anthesis and pollen tube growth suggests a crepuscular pollination strategy. Suspected pollinators have been observed on floral parts of theobromas possessing stomate type nectaries and various shaped trichomes (blade of petal ligule and adaxial surface of petal hood). H. purpurea has elongate ligules devoid of stomates. Glandular clublike structures are found on the ovaries of all three spp. In numerous spp. of theobromas, except T. cacao, and two species of Herrania, a conspicuous ring of multicellular trichomes occurs at the adaxial base of the sepals. A possible function for the ring may be fragrance production because of its greatly reduced condition in the faintly scented T. cacao and the prevalence of pronounced fragrances in these other species.     

CHROMATOGRAPHIC COMPARISON OF TRAGOPOGON SPECIES AND HYBRIDS

Approximately 1,700 plants representing five species of Tragopogon (Compositae) and their F₁ and F₂ hybrids were analyzed by two-dimensional descending paper chromatography. Each species, or population within a species, was chromatographically distinct. Often, however, the differences were more quantitative than qualitative. The chromatographic data generally supported the species relationships which had been determined from previous morphologic, hybridization, and fertility studies. Inheritance of the flavonoid compounds was usually additive in the F₁'s. Segregation and recombination of the genes controlling the synthesis of these compounds sometimes approximated 3:1 or 9:7 ratios in the F₂'s. Occasionally parental compounds were missing from some of the hybrids. “Hybrid” compounds which had not been found in either parent were absent from the F₁ but did occur in several F₂ populations. Two linkage groups were present. The first contains genes controlling the synthesis of three compounds and the second, four compounds.     

CHROMATOGRAPHIC COMPARISON OF DICENTRA SPECIES AND HYBRIDS

Ten species of Dicentra were examined by two-dimensional descending paper chromatography. The flavonoid components, including anthocyanins, formed patterns which were specific to a species or a group of closely related species, and these confirmed certain natural relationships within the genus. Some of the components were hydrolyzed and close structural relationships among them were revealed. They were further characterized by spray reactions and R_F measurements in a variety of solvent systems. The inheritance of the components, especially of the anthocyanins, was studied in the hybrids. All parental substances appeared in some hybrids, but in others some parental components were missing. “Hybrid substances” which had not been present in either parent were found in certain hybrids. This is thought to represent either reconstruction of ancestral biosynthetic pathways, probably through genic complementation, or extension of existing synthetic routes through some type of interaction between parental genomes.     

ROLE OF PSEUDOBULBS IN GROWTH AND FLOWERING OF CATASETUM VIRIDIFLAVUM (ORCHIDACEAE)

In Catasetum viridiflavum Hook., a drought-deciduous orchid from central Panama that produces unisexual flowers, plants possess up to nine annually-produced pseudobulbs. I investigated the role of these structures in plant growth and flowering by 1) relating annual shoot size and flower production to the size and number of pseudobulbs possessed by plants, 2) experimentally severing connections between young and old pseudobulbs when plants were dormant and monitoring their subsequent vegetative growth and flowering, and 3) determining the seasonal variation in water content, total nonstructural carbohydrates, nitrogen, and phosphorus in pseudobulbs. In small plants (1 to 3 pseudobulbs) pseudobulb stores appeared important to both vegetative growth and flowering. In larger (= older) plants, pseudobulb number was not related to vegetative growth and experimental separations of young from old pseudobulbs did not affect growth. However, flower production by experimental plants was significantly reduced relative to controls. Male plants were usually smaller than female plants in the areas studied; however, experimental reductions of pseudobulb number did not affect the sex expression of plants. All measured nutritional components of pseudobulbs exhibited significant seasonal variation. Carbohydrates appeared most important for supporting growth immediately following dormancy. Nitrogen and phosphorus were less important for this role and may have been more important for determining the number of flowers produced by plants.     

THE TUBERS,SAPOGENINS, AND VIRUS RESISTANCE OF DIOSCOREA SPECIES HYBRIDS

Dioscorea species differ in sapogenin content, tuber size and shape, and virus resistance. The amount and type of sapogenins in tubers of F₁ hybrids among four sapogenin-bearing and one other Dioscorea species were determined chromatographically. Characteristics of the tuber and resistance to a virus were observed and compared to those of the parents. The presence of particular sapogenins appeared to be a dominant trait modified by minor genes from either parent. Other traits appeared to be determined by many genes. Heterosis was expressed in some hybrids by superior yields and excellent virus tolerance. Some of the hybrids could be used as clonal varieties, but none contained the desired keto sapogenins except in mixtures with diosgenin.     

OVULE AND EMBRYO DEVELOPMENT IN DORITIS PULCHERRIMA (ORCHIDACEAE)

The placental ridge began to proliferate 10 days after pollination. Megaspore mother cell underwent meiosis to form two dyads at first division. At 50 days two megaspores and generating dyad were formed by second division. The functional megaspore divided successively three times to form an eight-nucleate embryo sac at 60 days. Double fertilization occurred forming the zygote and endosperm initial cell. However, the endosperm initial cell degenerate soon thereafter. The zygote divided to form a terminal cell, the middle cell and suspensor initial cell at 70 days. The terminal and middle cells successively divided to form a multi-celled embryo up to 120 days after pollination. Histochemical study showed that the stainability of DNA, RNA and total proteins were almost constant during ovule and embryo development. Stainability of total carbohydrates decreased.     

PEROXIDASE LOCALIZATION,ACTIVITY, AND ISOZYME PATTERNS IN THE DEVELOPING SEEDLING OF VANDA (ORCHIDACEAE)

Peroxidase activity in the seedling of Vanda was investigated at various stages of development. Active sites were demonstrated histochemically and soluble proteins and peroxidase isozymes were resolved by disc electrophoresis at progressive stages of growth. Activity, which is highest in the early stages of development and lowest at the stage when maximum differentiation occurs, is confined to the epidermal layer and outer surface of the seedling in early stages of development, It is also present in the vascular tissues of the leaves, root, and parenchymatous region at later stages. Indoleacetic acid raises peroxidase activity when present in the growth medium in physiological concentrations. The number of isoperoxidases varies with developmental stage and is lowest in the stage at which leaves and roots are initiated. These observations are discussed in relation to the hypothesis that the peroxidases play a role in morphogenesis as a part of the indoleacetic acid-oxidase system.     

GENOME RELATIONSHIPS OF INTRA- AND INTERSECTIONAL SPECIES HYBRIDS OF ONCIDIUM TRIQUETRUM

Chromosome numbers and meiotic behavior of six interspecific hybrids of Oncidium triquetrum were investigated. The somatic chromosome number of O. triquetrum (section Oncidium) x O. variegatum (section Oncidium) was 2n = 42. O. triquetrum x O. splendidum (section Plurituberculata) and O. triquetrum x O. cebolleta (section Cebolletae) were 2n = 39 and O. triquetrum x O. floridanum (section Planilabra), O. triquetrum x O. flexuosum (section Synsepala) and O. triquetrum x O. onustum, (section Onusta) were 2n = 49. The intersectional species hybrid, O. triquetrum x O. variegatum, showed fairly regular meiosis with a mean of 20.4 bivalents, indicating strong homology of parental genomes. In contrast, highly irregular meiosis with poor chromosome pairing was observed in all intersectional hybrids. The mean number of bivalents ranged from 1.8 to 9.5. On the basis of chromosomal affinity at metaphase I, O. triquetrum showed a close relationship to O. variegatum in the same section, but more distant relationships to O. splendidum, O. cebolleta, O. floridanum, O. flexuosum and O. onustum belonging to different sections.     

CYTOGENETICS OF AGROPYRON FERGANENSE AND ITS HYBRIDS WITH SIX SPECIES OF AGROPYRON,ELYMUS, AND SITANION

Meiosis and mode of reproduction are described in Agropyron ferganense Drob., a perennial forage grass from Central Asia. This species is diploid (2n = 14); it exhibits normal meiosis and reproduces by cross-pollination. Hybrids were produced between A. ferganense and six species with known genome formulas: 1) North American A. spicatum (Pursh) Scribn. & Smith, an SS diploid (2n = 14), 2) Middle Eastern A. libanoticum Hack., an SS diploid (2n = 14), 3) North American A. dasystachyum (Hook.) Scribn., an SSHH tetraploid (2n = 28), 4) Eurasian A. caninum (L.) Beauv., an SSHH tetraploid (2n = 28), 5) North American Sitation hystrix (Nutt.) J. G. Smith, an SSHH tetraploid (2n = 28), and 6) South American Elymus patagonicus Speg., an SSHHHH hexaploid (2n = 42). Almost complete chromosome pairing in the A. ferganense x A. spicatum and A. libanoticum hybrids demonstrated that A. fergenanse is an SS diploid, but it is genetically isolated from the other SS diploids because of high sterility in the F₁ hybrids. S-genome diploids form a network of species that extend from the Middle East through Central Asia to western North America. Frequent occurrence of seven univalents and seven bivalents at metaphase I in the triploid hybrids of A. ferganense x A. dasystachyum, A. caninum and S. hystrix was consistent with the proposed genome formulas of SS for A. ferganense, SSHH for the three tetraploid species, and SSH for the hybrids. Chromosome pairing was highly variable in the A. ferganense x E. patagonicus hybrids; however, some cells had almost complete bivalent pairing, an expected observation in an SSHH hybrid from a cross between an SS diploid (A. ferganense) and an SSHHHH hexaploid (E. patagonicus). Various options were considered concerning the appropriate generic classification of the S-genome diploids, which are now commonly placed in Agropyron. The inclusion of these species in the genus Eiytrigia, as advocated by some Soviet taxonomists, appears to be a reasonable decision.