THE ANATOMY OF TUMORS INDUCED ON CITRUS BY CITRUS VEIN-ENATION VIRUS

Citrus vein-enation virus-induced tumors on leaves, thorns, stems, and roots of Citrus auranti-folia (Christm.) Swingle and C. jambhiri Lush. were investigated. Leaf vein tumors are initiated as cytological abnormalities of phloem fiber primordial cells adjacent to protophloem sieve tubes. The tumors then enlarge through hyperplasia of the affected fiber primordia. The mesophyll and epidermal tissues on the abaxial side of affected veins divide less prolifically and contribute to the tumor mass. Leaf vein tumors are determinate, like the protophloem where they originate, and cease enlarging as the leaf matures. Most thorn tumors are initiated in fiber primordia and develop similarly to vein tumors. Stem tumors and some thorn tumors develop from affected cells of the procambial tissue that lies between the metaxylem and metaphloem of vascular bundles. The cambium which differentiates in these areas is composed of affected cells and produces large amounts of abnormal xylem tissue. The resulting woody tumors are indeterminate like the cambium and secondary xylem.     

THE EFFECTS OF RELATIVE HUMIDITY AT THE TIME OF FLOWERING ON FRUIT SET IN BEAR OAK (QUERCUS ILICIFOLIA)

Fifty-six randomly selected bear oak trees were moved into growth chambers to determine the influence of relative humidity at the time of flowering on fruit set. The effect of humidity greater than 61 % was to greatly reduce fruit set. Trees which were kept in a chamber where relative humidity was less than 50 % had significantly higher fruit set.     

UNDERGROUND SYSTEMS OF GAMBEL OAK (QUERCUS GAMBELII) IN CENTRAL UTAH

Excavation to a depth of 1 m of a 3 × 4 m portion of a clone of Quercos gambelii revealed the presence of a massive underground system of lignotubers, interconnecting rhizomes and roots. Lignotubers comprised the greatest proportion (72%) of the total below ground biomass (81 t/ha). Lignotubers are distinctive in appearance: they are an enlarged stemlike structure with numerous clusters of adventitious buds on the surface. Anatomically, they are comparable to the above ground stems with growth rings. Lignotubers are lobed and distorted, giving the appearance of a burl. Rhizomes are round to I-beam in shape with a star-shaped pith, distinct annual rings, bud traces, and branch gaps. There were also clusters of adventitious buds on rhizomes, although not as dense as those on the lignotubers. Roots are oval in cross section with discernible growth rings, no pith, and no bud traces.     

SITE-SPECIFIC CHANGES IN THE BARK TEXTURE OF QUERCUS FALCATA MICHX. (SOUTHERN RED OAK)

A method of measuring bark texture is described. This method is used to show that bark roughness in Quercus falcata Michx. (southern red oak) increases from mesic to xeric sites. This change does not appear to be explained by variability in tree size and age, or by changes in the relative abundances of varieties falcata and pagodaefolia. We suggest that it may be due to postulated relationships between bark texture (or the associated property of outer bark thickness) and tree fire resistance, nutrient conservation or susceptibility to pathogens.     

ONTOGENY IN MONOCOTYLEDONS AS REVEALED BY STUDIES OF THE DEVELOPMENTAL ANATOMY OF PERICLINAL CHLOROPLAST CHIMERAS

The developmental anatomy of apically stable periclinal chloroplast chimeras was studied in a number of monocotyledonous genera. Their ontogeny is basically similar to that of dicotyledons. In both there are three independent apical layers (L-I, L-II, and L-III) whose derivatives can be traced in stem, leaf and flower. The bulk of the stem tissue is derived from L-III with only the epidermis and one or two hypodermal cell layers from L-I and L-II. All three layers participate in formation of the leaf with great flexibility in the amount of tissue from each. There is more instability in growth of most monocotyledonous leaves than in dicotyledonous leaves. As a result there is relatively more tissue derived from L-I and L-II and less from L-III. The same is true in floral development so that a significant number of gametes are of L-I origin. As in dicotyledons, there is variation in direction, timing, and frequency of cell division. However, an overriding genetic control results in normal size, shape, and structure. The evidence from genetic and cytochimeras in both monocotyledons and dicotyledons has provided direct experimental proof of the functional reality of the apical layers described by Hanstein and Schmidt.     

DEVELOPMENTAL ANATOMY AND HISTOCHEMISTRY OF LIGHT-INDUCED CALLUS FORMATION BY DIÖON EDULE (ZAMIACEAE) SEEDLING ROOTS IN VITRO

Light exposure caused massive areas of callus to develop from primary roots of aseptically cultured Diöon edule seedlings. Callus initiation and continued growth was due to cortical cell hypertrophy and subsequent periclinal cell division. Callus initiation occurred in the subdermal cortex and developed radially and centripetally from the locus of initiation. Callus formation encompassed virtually all of the cortex, but did not incorporate any of the vascular tissues. With very large calluses, sectors of internal periderm arose between the developing callus and the remaining quiescent cells of the inner cortex. Most of the callus cells were typical, vacuolate parenchyma with cellulose walls, and large, multilobed amyloplasts. Callus also contained idioblasts with globular deposits of polyphenols. Adjacent cortical cells were typical parenchyma with peripheral cytoplasm, but contained small plastids with little starch accumulation.     

DEVELOPMENTAL ANATOMY AND ULTRASTRUCTURE OF THE ANT-FOOD BODIES (BECCARIIAN BODIES) OF MACARANGA TRILOBA AND M. HYPOLEUCA (EUPHORBIACEAE)

Macaranga is a common secondary growth tree of S.E. Asia. Nine species possess hollow stems which harbor an ant colony, and also produce food bodies which are eaten by the ants. In return, the ants protect the plant from herbivore damage. The multicellular food bodies of M. triloba (Bl.) Muell. Arg. are developed on the underside of down-turned clasping stipules, while in M. hypoleuca (Reichb. f. and Zoll.) Muell. Arg. they are produced on the abaxial surface of young leaves. Food body cells of both species are very rich in lipid, contain large starch grains, and possess an electron-dense hyaloplasm. It is proposed to name the Macaranga ant-food bodies Beccariian bodies in honor of the Italian botanist Odoardo Beccari who explored S.E. Asia in the late 1800s.     

CHANGES IN THE ULTRASTRUCTURE OF XYLEM PARENCHYMA CELLS OF PEACH (PRUNUS PERSICA) AND RED OAK (QUERCUS RUBRA) IN RESPONSE TO A FREEZING STRESS

An ultrastructural investigation was conducted of xylem parenchyma cells of peach (Prunus persica [L.] Batsch.) cv. Harbrite and red oak (Quercus rubra L.) in response to a freezing stress. Freezing curves of xylem tissues, as determined by differential thermal analysis, were used to predict temperatures at which both living and dead cells would be observed. Tissues were exposed to low temperatures (-15 to -35 C) and fixed in a frozen state at -10C and at thawing. Current models of the freezing behavior of supercooled plant cells suggest that xylem parenchyma cells behave as individual water droplets. This implies that cells are unresponsive to the presence of low temperature and extracellular ice until internal nucleation triggers lethal, intracellular freezing. For these reasons, deep supercooling has been described as an avoidance mechanism. Results of this study confirmed earlier reports that xylem parenchyma cells freeze as individuals or in small groups. Individual cells, however, did not exhibit a neutral response. Instead, a range of responses was observed that included internal and external vesiculation, deep invaginations of the plasma membrane, and the formation of electron-dense deposits external to the plasmalemma. In general, our observations suggested that the cells responded to a dehydrative stress. Results are discussed in context of the biophysical data associated with deep supercooling phenomena and compared to responses of cells that exhibit extracellular freezing.     

A NEW SPECIES OF BLACK OAK (QUERCUS,SUBG. ERYTHROBALANUS,FAGACEAE) FROM THE SIERRA MADRE OCCIDENTAL,MEXICO

Quercus mcvaughii is described as a new species of black oak (subgenus Erythrobalanus) from the Sierra Madre Occidental, in northern Durango and western Chihuahua, Mexico. It is most closely related to the more southern Q. crassifolia. Sessile or subsessile hairs, usually of different sizes, on the abaxial leaf surface distinguish Q. mcvaughii from Q. crassifolia, where hairs are similar in size and conspicuously stipitate. A key is provided for distinguishing similar species in the region. Intergradation of Q. mcvaughii with Q. crassifolia, Q. hypoleucoides, and Q. sideroxyla is reported.     

DEVELOPMENTAL ANATOMY OF DIRECT SHOOT ORGANOGENESIS FROM LEAF PETIOLES OF VITIS VINIFERA (VITACEAE)

The anatomy of direct shoot organogenesis from leaf petioles of Vitis vinifera cv. French Colombard cultured in vitro was studied by light microscopy. Regenerating petiole stubs were fixed at 2- or 3-day intervals and sectioned longitudinally. By day 3 on regeneration medium, new cell divisions were observed. After 6 days, three distinct regions of meristematic activity were apparent within the expanding petiole stub: the wound-response, organogenic, and vascularization regions. In the organogenic region, rapid periclinal divisions of vacuolate outer cortical cells formed nodular bumps, many of which developed vascular strands and marginal meristems and formed adventitious leaves. Promeristems with small, densely staining cells and a distinct tunica layer also originated in the organogenic region, by cell division in the epidermal and subepidermal cell layers. With vascularization and the formation of leaf primordia, many promeristems became adventitious shoot meristems. Adventitious leaves and promeristems were initiated continuously from day 10 until day 33. Promeristems were often initiated near or upon adventitious leaves but could form either before or after the adventitious leaf developed. Adventitious leaves and shoot meristems developed vascular connections with the vascular bundles of the original expiant. The implication of this pattern of regeneration for Agrobacterium-mediated transformation of Vitis is discussed.     

ETIOLOGY AND DEVELOPMENT OF HYPERPLASIA INDUCED BY STREBLONEMA SP. (PHAEOPHYTA) ON MEMBERS OF THE LAMINARIALES (PHAEOPHYTA)1

Filaments of Streblonema sp. isolated from hyperplasia (galls) on Nereocystis luetkeana (Mert.) Post. et Rupr. induced similar gall growths when inoculated on young sporophytes of Nereocystis luetkeana, Macrocystis integrifolia Bory, and Laminaria japonica Aresch. Filaments were irregularly branched and uniseriate with cells 5–8 μm in diameter and 10–30 μm long. Growth under varied cultured conditions produced unilocular sporangia. Zoospores released from the sporangia germinated into identical filaments which also formed unilocular sporangia. Gall tissue originated from the innermost cells of the epidermal meristematic zone. When infected these cells divided in an irregular and unorganized manner. The resulting structure was a pronounced departure from normal morphology.