CULTURE AND DEVELOPMENT OF HILDENBRANDIA RIVULARIS FROM DENMARK AND NORTH AMERICA

Hildenbrandia rivularis was collected in Denmark and the United States. The life history of this encrusting red alga is described on the basis of unialgal cultures maintained for more than 2 years. Significant changes in cellular and colonial morphology are reported. Events of the life history (i.e., reproduction by stolons, fragmentation, or gemmae; and manner of branching) which were previously in question or unknown are clarified. Mechanism(s) of certain morphogenetic phenomena remain obscure (cell wall and plastid ontogeny). These and related problems are now under investigation. Hildenbrandia should be added to the freshwater algal flora of the United States.     

CYTOGEOGRAPHY OF PANICUM VIRGATUM IN CENTRAL NORTH AMERICA

Mc Millan , Calvin . (U. Texas, Austin.), and John Weiler . Cytogeography of Panicum virgatum in central North America. Amer. Jour. Bot. 46(8): 590–593. Illus. 1959.—For 124 clones of Panicum virgatum L. representing 44 local populations from Manitoba and eastern Montana to Texas, the chromosome number was determined. Most of the clones were grown in a transplant garden at Lincoln, Nebraska. Among the earlier-flowering clones from the northern and western area, a preponderance were tetraploids (n = 18). Among the later-flowering clones, the Iowa material was predominantly tetraploid, while those from Nebraska presented a diversity of types (n = 18, 27, 36) within each population. A series of polyploids was common in population samples from southern Kansas, Oklahoma, and Missouri. Through the complex breeding patterns resulting from the common occurrence of a range of polyploidy and the possible action of apomixis, variability within the population is maintained, and with it, genetic insurance for survival in highly unpredictable prairie habitats.     

BIOGEOGRAPHY OF STREAM MACROALGAE IN NORTH AMERICA1

In a survey of 1000 20-m long stream segments in North America from 73°N to 10° N, 259 infrageneric taxa were identified, composed of 35% Chlorophyta, 24% Cyanophyta, 21% Chrysophyta, 20% Rhodophyta, and one species of Phaeophyta. The most common morphological forms were mats (42%), gelatinous colonies (23%), and gelatinous filaments (13%); the majority of taxa were vegetative (78%). The frequency of reproductive states varied among the biomes examined, with the highest values observed as follows: vegetative (85%) in the tundra, sexual (35%) in the deciduous forest, and asexual (21%) in the tropical rainforest. In terms of total species, the tundra had the lowest number (54), the boreal forest had the greatest number (100), and other well-sampled biomes had 84 to 87. The Chlorophyta had the greatest species numbers in all biomes, and the relative contribution of this division did not vary significantly throughout the continent. With regard to similarity of species composition, the two closest associations were the boreal forest with the western coniferous forest and the eastern hemlock–hardwood forest with the deciduous forest. Species numbers per stream segment ranged from 0 to 11 (X?= 3.1), cover ranged from 0 to 100% (X?= 15%), and there was no significant difference in these values among the biomes. The cyanophyte Phormidium retzii (C. Ag.) Gom. was the most widespread species (in 172 segments and all biomes). The majority of species were found in moderate current velocities (X?= 40 cm X? s^?1), neutral to slightly alkaline pH (X?= 7.5), and moderately low ion waters (X?= 261 μS · cm^?1). On both tropical and Arctic islands, there was no significant increase in total species or species numbers per stream segment with increasing surface area.     

WOOD OF GINKGO IN THE TERTIARY OF WESTERN NORTH AMERICA

Scott , R. A., E. S. Barghoorn , and U. Prakash . (U.S. Geol. Sur., Denver, Colo.) Wood of Ginkgo in the Tertiary of western North America . Amer. Jour. Bot. 49(10): 1095–1101. Illus. 1962. —Woods of Ginkgo and extinct related genera are very rare in the fossil record in contrast to the numerous ginkgoalean leaves. Ginkgo wood may be distinguished from other gymnosperms by a combination of anatomical features herein described. Ginkgo wood from beds of Miocene age at Vantage, Washington, first identified by Beck, is assigned to a new species, G. beckii. Ginkgo wood from the upper Eocene Clarno Formation, John Day Basin, Oregon, is described as G. bonesii sp. nov. Scarcity of fossil ginkgoalean woods may reflect unusual susceptibility to degradation of their cell walls in contrast to the greater chemical resistance to degradation which features many coniferous woods.     

A RECORD OF PAULOWNIA IN THE TERTIARY OF NORTH AMERICA

Smiley , Charles J. (Macalester Coll., St. Paul, Minn.) A record of Paulownia in the Tertiary of North America. Amer. Jour. Bot. 48(2): 175–179. Illus. 1961.—Paulownia, an eastern Asiatic genus in the family Scrophulariaceae, has been identified from fossil leaves in the Ellensburg flora of Washington. Age of these fossils is late Miocene (Barstovian) to early Pliocene (Clarendonian). They are nearly identical to leaves of the living P. tomentosa (Thunberg) Steudel, a deciduous tree now growing in temperate parts of China and one that has escaped from cultivation in eastern United States. Identification is based on comparative leaf morphology. Modern and fossil Paulownia leaves may be distinguished from those of such other genera as Buettneria, Catalpa, and Cercis by secondary and tertiary venation. Central Washington environment during this time was well suited to the growth and reproduction of Paulownia, judging from such fossil associates as Liquidambar, Nyssa, Passiflora, Persea, Rhododendron, Ulmus, and Zelkova. Deciduous habit, present temperate environment, possible early Tertiary record in Alaska, later Tertiary records in middle latitudes of North America and Europe, and present occurrence in China indicate that Paulownia was once widely distributed over the northern hemisphere. Secular climatic trends toward cooler conditions since the Eocene appear to have resulted in the southward migration of Paulownia as a member of the Arcto-Tertiary Geoflora. Subsequent extinctions in Europe and North America may have resulted from Pleistocene glacial climates, and from barriers to further migrations to more southern latitudes.     

FOSSIL OPHIOGLOSSALES IN THE PALEOCENE OF WESTERN NORTH AMERICA

Vegetative and fertile frond segments of Botrychium have been recovered from Paleocene deposits of central Alberta, Canada. Specimens are preserved as coalified compressions that yield information about frond structure, sporangia, and spore ultrastructure. These fossils, described as Botrychium wightonii sp. nov., establish a megafossil record for the Ophioglossales, and demonstrate that modern-appearing species of the order were present in western North America by the earliest Tertiary. The largest vegetative fragments are up to 4.6 cm long and tripinnately compound, with opposite to subopposite branching. Ultimate segments are pinnatifid with dentate pinnules and open dichotomous venation. Fertile specimens are also tripinnately compound with a long rachis and subopposite to alternate pinnae. Sporangia are either submarginal and superficial, or marginal, and are all directed toward one surface of the pinnule. They are ovoid to subspheroidal and 0.8-2.0 mm in diameter. Some sporangia are apparently stalked, while others appear to be sessile. This variation results both from the ultimate frond segments being compressed in several different planes, and the fossils being exposed at different levels. Spores macerated from the sporangia are radial and trilete, and range 30–67 μm in diameter. Most are psilate, but some have a densely striate surface.