POLLINATION OF THE ARROYO WILLOW,SALIX LASIOLEPIS: ROLE OF INSECTS AND WIND

We studied the relative roles of insects and wind as pollen vectors for the arroyo willow, Salix lasiolepis Benth. through insect exclosure studies at two elevational sites. Insect pollination resulted in production of 99.9% of seeds at a low elevation site (2,130 m) and at a high elevation site (2,450 m) with wind playing an exceedingly small role. Few pollen grains reached individual pistillate catkins despite the presence of abundant airborne willow pollen near male plants. In flowers that showed evidence of receipt of wind transferred pollen, due to their swollen appearance, we found only 1.74 fertilized ovules per flower and that 90.9% of these fertilized ovules were aborted by the maternal plant. In contrast, flowers open to insect visitation possessed 7.00 fertilized ovules per flower, 83.3% of which became filled seeds. We tested for the existence of apomictic seed production through use of closed bags that excluded both insect-and wind-transferred pollen but found no evidence of seed produced in this treatment. Additional control studies documented that wind treatment bags did not impede pollen flow while neither wind or closed bags influenced seed set in our treatments.     

DEVELOPMENT OF THE CUTICULAR LAYERS IN ANGIOSPERM LEAVES

Schieferstein , R. H., and W. E. Loomis . (Iowa State U., Ames.) Development of the cuticular layer in angiosperm leaves. Amer. Jour. Bot. 46(9): 625–635. Illus. 1959.—The cuticularized layers of leaves and other plant surfaces consist of a primary cuticle, formed by the oxidation of oils on exposed cell walls, plus various surface and subsurface wax deposits. The primary cuticle appears to form rapidly on the walls of any living cell which is exposed to air. Surface wax is present on the mature leaves of about half of the 50 or 60 species studied. In general, wax is extruded at random through the newly formed cuticle of young leaves and accumulated in various reticulate to semicrystalline patterns. No wax pores through the cuticle or primary wall can be observed in electron-micrographs of dewaxed mature leaves. Wax accumulations on older leaves are generally subcuticular and may involve the entire epidermal wall. These deposits appear to be of considerably greater ecological significance than those on the surface. Isolated cuticular membranes from Hedera helix increased slightly in permeability to water with age of the leaf, but permeability to 2,4-D decreased 50 times. Evidence based on the patterns of cellulose in primary walls, of surface wax on growing leaves, of the appearance of the cuticle at the margins of growing epidermal cells, of the forms of the cuticle plates digested from growing and older leaves, and of the marginal location of new wax deposits on growing maize leaves is presented to support the thesis that the enlargement of the outer surface of the epidermal cells of leaves occurs at the margins of the surface. Earlier formed cuticle and wax are thus undisturbed during growth. These observations, coupled with evidence for apical growth in fibers, root hairs, etc. suggest that the primary walls of angiosperm cells are formed in specific, localized growth regions, rather than by plastic extension and apposition.     

GENETIC BLOCKS IN THE THIAMINE SYNTHESIS OF THE ANGIOSPERM ARABIDOPSIS,,

Five thiamine-requiring mutants were obtained at two loci. Two are blocked in the synthesis of the pyrimidine part of the vitamin, the other three have lost the ability to make the thiazole moiety. None of the tested substances suggested as possible or likely precursors of the pyrimidine or the thiazole components of thiamine displayed any activity in the mutants. These conditional lethals responded to remarkably small supplements of thiamine. The pyrimidine-requiring mutants utilized to some extent the anti-vitamin neopyrithiamine. The thiazole-less mutants grew on basal media supplemented only with the analog, oxythiamine. Thiamine deficiency, irrespective of the position of the genetic block in the synthesis, results in a characteristic anomaly of pigmentation. The position of the py locus in the second linkage group has been determined. Allelic complementation has not been detected. The frequency of mutations affecting thiamine synthesis appears about the same in Arabidopsis as in fungi. The general frequency of reparable genetic lesions is, however, one to two orders of magnitude lower in Arabidopsis than that in fungi or bacteria.     

SURGICAL CONSIDERATIONS IN DISEASES OF THE PANCREAS

Present data indicate that surgical treatment of pancreatitis is most successful in cases in which the disease is caused by extrahepatic disease of the biliary tract.Operation is also effective in cases of islet cell tumors, cysts, lithiasis, trauma and annular pancreas.Results seem to justify radical operation for early carcinoma of the ampulla of Vater and pancreas.The value of surgical treatment in other lesions of the pancreas is doubtful.