PHOTOSYNTHESIS IN THE ANOMALOUS SECONDARY WOOD OF ATRIPLEX CONFERTIFOLIA STEMS

The anomalous secondary wood of A triplex confertifolia stems consists of vascular strands of xylem, phloem, and parenchyma embedded in fiberous conjunctive tissue. The included parenchyma contains chloroplasts and is capable of photosynthesis, as measured by¹⁴CO₂ uptake by wood in the light.     

EVOLUTIONARY STUDIES OF ATRIPLEX: CHROMOSOME RACES OF A. CONFERTIFOLIA (SHADSCALE)

Atriplex confertifolia (Torr. and Frem.) S. Wats., a species endemic to western United States, occurs as 2n, 4n, 6n, 8n and 10n chromosome races. In the Great Basin, diploids occur altitudinally above the upper levels of Pleistocene lakes; the polyploids are in valley bottoms and sides. Diploids are larger in all respects than tetraploids, hexaploids, and octoploids. Decaploids are the most robust of all. Diploids can be distinguished in early seedling stages by having broader leaves and shorter internodes than polyploids. Polyploid plants are currently produced sporadically in natural populations and appear to be easily generated by unreduced gametes. Most polyploid populations in the Great Basin apparently arose recently and erupted into extensive stands because of the sudden availability of large, relatively uniform domains provided by the disappearance of Pleistocene lakes.     

EVOLUTIONARY STUDIES OF ATRIPLEX: PHYLOGENETIC RELATIONSHIPS OF ATRIPLEX PLEIANTHA

Atriplex pleiantha Weber differs from all other species of Atriplex in having 1) multiple female flowers subtended by two bracts, 2) female flowers with a perianth, and 3) embryos with radicles pointing downwards. Because of these significant differences it is proposed that Atriplex pleiantha be elevated to the level of a separate genus and be designated Proatriplex pleiantha (Weber) Stutz & Chu. The closest relatives of Proatriplex appear to be Archiatriplex, Endolepis, Exomis, and Microgynoecium. These are all diploid, monoecious annuals, have non-Kranz type leaf anatomy, and female flowers with a perianth.     

EVOLUTIONARY STUDIES OF ATRIPLEX: A RELIC GIGAS DIPLOID POPULATION OF ATRIPLEX CANESCENS

Growing on shifting sand dunes in central Utah is a small endemic population of a gigas form of A triplex canescens. Whereas normal A. canescens usually grows to a height of three to four feet and occasionally to five or six feet, the gigas form often reaches ten and sometimes twelve feet. All normal A. canescens so far examined (67 populations) have 2n = 36 chromosomes; the gigas form has 2n = 18 chromosomes. Several lines of evidence suggest that the gigas form is a relic diploid and the normal form is an autotetraploid derived from it. The growth rate of seedlings and new twigs is nearly twice as great in the diploid as in the tetraploid. Seed germination is faster and much better in the diploid. The tetraploid is reproductively isolated from the diploid because of a much earlier flowering period. The diploid plants possess many attributes which make them uniquely adapted to the drifting sand dune habitat.     

FIBRILLAR DIFFERENTIATION IN MYXOMYCETE PLASMODIA

Myxomycete plasmodia of four different types (not including Physarum polycephalum) were studied in thin sections viewed in the electron microscope. In the cytoplasm of the protoplasmodia of Clastoderma debaryanum and the phaneroplasmodia of Fuligo septica fixed in situ, fibrillar differentiations of three rather distinct kinds were observed. One of these is filamentous and closely resembles the filaments (or "microtubules") of the mitotic apparatus of other species. The larger phaneroplasmodia of two species belonging to the Physarales and the plasmodium of Hemitrichia vesparium showed fewer and less well defined fibrils, and no fibrils were seen in the aphanoplasmodium of Stemonitis fusca. Good stabilization of such fibrils in larger plasmodia may require fixation methods more rigidly controlled than those which succeed with microscopic protoplasmodia. The function of the observed fibrils cannot yet be determined. Their presence in cytoplasm fixed in situ, however, lends support to those theories of protoplasmic movement which are dependent on integral cross-bonding of one or a few molecular species.     

CHROMOSOMAL DIFFERENTIATION IN CLARKIA DUDLEYANA

Snow , Richard . (U. California, Davis.) Chromosomal differentiation in Clarkia dudleyana. Amer. Jour. Bot. 47 (4) : 302—309. Illus. 1960.—Clarkia dudleyana (n=9) is a common, colonial annual of the early-summer California flora. Of 275 individuals, derived from 9 natural populations and their garden-grown representatives, 17.1% were heterozygous for reciprocal translocations. Supernumerary chromosomes were also found in about 2% of the plants examined. The translocation heterozygotes are not distributed regularly over the species range but are concentrated near the geographical center of distribution. Most of the populations contained none or only a few heterozygotes, but in one colony 69% of 42 plants sampled were heterozygous. Judging from the meiotic metaphase associations observed, at least 5 different chromosome arrangements are present at this locality. Hybrids between colonies have invariably been translocation heterozygotes, the largest association found in such hybrids being a chain of all 18 chromosomes (a potential ring of 18). No correlation is evident between geographical separation and degree of cytological differentiation. Heterozygotes with smaller rings of 4 or 6 chromosomes, whether from natural populations or resulting from interpopulation hybridization, are highly fertile owing to the regular alternate disjunction of the chromosomes of the rings. In the larger rings of 12 to 18 chromosomes, derived from interpopulation crosses, segregation is much more irregular and leads to high sterility. It is possible that at least in some localities the heterozygotes enjoy a selective advantage over their homozygous sibs. It is also postulated that homozygosity for a particular chromosome arrangement may be selectively favored in a certain habitat, as a result of a position effect attendant upon placing formerly non-linked genes in the same linkage group through reciprocal translocation. The high degree of chromosomal differentiation between some populations of this species suggests that the complex heterozygotes of Oenothera have arisen as a result of hybridization of cytologically differentiated races.     

GEOGRAPHIC VARIATION IN GENTOO PENGUINS PYGOSCELIS PAPUA

Field and museum measurements confirm the existence of a morphologically distinct southern subspecies of Gentoo Penguin Pygoscelis papua ellsworthi , breeding on the Antarctic Peninsula and the South Orkney and South Shetland Islands. Morphological and zonal differences between other island stocks are noted, but present evidence does not support further definition of subspecies.