Alaria marginata Postels and Ruprecht has a sieve tube system which extends through the lamina, especially the midrib, and through the stipe. The sieve elements originate from the innermost cortex cells and are nucleate, highly vacuolated cells that contain the usual cell organelles and membrane systems. The plastids and mitochondria show some special features in their morphology and fine structure. P protein is absent. Sieve pores, 0.11–0.3 μm in diameter, occur in cross walls between two sieve elements. They are lined by plasmalemma, and the cytoplasms of the two cells are interconnected through them. Long-distance transport of photo-assimilate follows the source–sink relationship; but its normal basipetal direction can be reversed by creating "artificial" sinks. Translocation velocity is in the range of 25 to 40 cm/h. The translocate consists mainly of mannitol and free amino acids, which were analyzed qualitatively and quantitatively. Double-labeling experiments with 32P and 14C indicate that inorganic ions are not translocated together with the 14C-labeled photoassimilates and probably move only by diffusion.

Srivastava, L. M., and K. Esau. (U. California, Davis.) Relation of dwarf mistletoe (Arceuthobium) to the xylem tissue of conifers. I. Anatomy of parasite sinkers and their connection with host xylem. Amer. Jour. Bot. 48(2): 159–167. Illus. 1961.—The anatomy of the sinkers of Arceuthobium infecting 7 species of conifers was studied by the use of serial cross, radial, and tangential sections of the host wood. The sinkers were found to be composed of parenchyma cells only, or of parenchyma cells and tracheary elements, including vessel elements. In all species tracheary cells of the sinkers had direct contacts with the host tracheids of axial and radial systems. Typically the sinkers were associated with rays of the host wood. In some species, the centripetal ends of sinkers were wedged in radially among the axial tracheids of the host, but centrifugally such sinkers were usually found associated with rays. In the region of the host cambium the sinker contained parenchyma cells meristematic in appearance and, in 6 out of 7 species, also mature tracheary elements. The oldest of these elements became stretched and ruptured, a circumstance indicating that growth occurred in the part of the sinker embedded in the host cambium. This growth appeared to be coordinated with that of the host cambium, so that the sinker became embedded in the host xylem and phloem. Radial centripetal penetration of sinkers among differentiating axial tracheids of the host possibly occurred to a limited extent.

Differentiation of vessel elements in corn is accompanied by marked changes in nearly all organelles except plastids. The young cells increase in volume and apparently synthesize new cytoplasmic protein. The initiation of wall thickening is accompanied by an aggregation of microtubules in specific locations and an increase in the number of mitochondria and dictyosomes. During the period of active wall deposition, the endoplasmic reticulum (ER) shows a highly elaborate form, harbors intralamellar tubules, and nearly blankets those parts of the wall which remain unthickened. Dictyosomes seem to produce at least two types of vesicles, one of which may serve as a carrier of lignin precursors. The final autolysis involves a progressive removal of vacuolar membranes, plastids, dictyosomes, vesicles associated with secretion of noncellulosic polysaccharides, microtubules, and finally plasmalemma, parts of cell wall, and cytoplasm. Mitochondria and ribosomes are degenerated. The ER probably plays an important role in this autolysis. The parenchyma cells associated with vessel elements are rich in mitochondria.

The large kelp Macrocystis integrifolia and Nereocystis luetkeana off the coast of British Columbia have light saturation points at about 200 foot candles (1 foot candle = 10.76391 lx); however, photosynthetic rates remain unimpeded through mugh higher light intensities, up to 7000 foot candles. Short-term labelling experiments indicate that the Calvin cycle is operational in these plants, but, in addition, and particularly in the young growing parts, relatively high activities of phosphoenolpyruvate carboxykinase (PEP-CK)and correspondingly high rates of 14C fixation in the dark are observed. In older, mature parts, the activity of PEP-CK as well as the ability for light-independent 14C assimilation are lower. These observations are supported by data from a variety of other Pacific Laminariales. Pulse–chase experiments in the light and in the dark reveal characteristic differences between young and mature parts of the fronds: apart from qualitative difference in the soluble fraction of assimilates, the young parts show a significantly large proportion of radiocarbon confined to the ethanol-insoluble fraction.

A dejned medium (MAM) simulating acid mine drainage waters was developed which supported reproducible growth rates of three axenic strains of Euglena mutabilis Schmitz. Growth responses to various pHs and carbon sources were examined under defined culture conditions. A lab strain and two5eld isolates, tested over PH range 1.5-9.0, grew best under acidic conditions (pH < 5.5) with highest growth rates at PH 3-4. Photoauxotrophic growth rates of all strains at PH 3 were improved sign? icantly ovcr unstirred batch controls by bubbling with air and even more by enrichment with 5% CO, i n air. These results conjrmed inorganic carbon limitation in batch culture. Organic carbon substrates were tested as possible carbon supplements in batch culture at pH 3. None of the strains survived in the dark on any of the twenty organic sources added. I n the light, the lab strain exhibited some photoheterotrophic growth potential 011 glucose, sucrose, ethanol, and amino acids but growth was inhibited by acetate. Field strains showed little or no growth improvement with any organic substrate addition. Under simultaneous enrichment with acetate and 5% C O , acetate continued to be inhibitory. Simultaneous enrichment with glucose and 5% CO, gave higher yields Ofthe lab strain than with CO, alone but did not enhance growth of the field strain. W e conclude that E. mutabilis is a n acidophilic photoauxotroph which appears unable to use or-#