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Stipular bud (SB) formation occurred spontaneously on \"Gorella\" strawberry leaf stipules during proliferation phase on Boxus medium. These buds gave rise to normal shoots on the inner median zone between the stipule tips. Some stipular buds also have been observed on other parts of adaxial surface of the stipule. Stipular bud formation took place directly on the stipule without an intermediate callus. The first stage consisted of subspherical protrusions of small cells which progressively differentiated into shoots that were able to proliferate and to root. Scanning electron microscopy was used to examine the developmental stages of this adventitious organogenesis and to describe morphologic abnormalities, e.g., multiapex formation and fasciation. In vitro cloning of plantlets was made from axillary and SBs produced by the same tufts. The greater flowering abundance of stipular plants resulted in a drastic reduction of the commercial production and the fruit caliber when compared to axillary plants. However, the general phenotype of the mother cultivar (Gorella) was not affected in either case.

Chicory root, stem, and leaf tissues have the propensity to regenerate organogenetic nodules following a wounding treatment. Using histological methods, we described this phenomenon on leaves of Cichorium intybus L. cv. 'Witloof' cultivated in vitro. Nodule morphogenesis and bud regeneration from nodules were characterized with the assistance of light and transmission microscopy techniques. Semithin and ultrathin sections of leaves and nodules were prepared from nodule induction to bud regeneration phases. Starch and inulin in differentiating tissues were histochemically detected in semithin and handmade sections. Our study demonstrates that nodules are formed in direct contact with vascular bundles of the leaves. The nodules consist of organized structures: a vascular center is surrounded by a large parenchyma, which is delimited by a periderm of multiple cork cell layers. Inside the vascular center near phloem tissues, a secretory network of articulated pseudolaticifers develops. From parenchymatous cells, in the vicinity of vascular centers, endogenous buds can be induced. In this region, several cords of vessel initials formed the vascular connection between neoformed buds and vascular centers. Simultaneously, transfer cell specialization occurs near the neoformed vascular strands. Vascular centers play a major role in this kind of organogenesis. Sugar metabolism appears to be closely related to nodule morphogenetic events.

Short-term cultures of bovine leukemic lymphocytes release virus particles with biochemical properties of RNA oncogenic viruses. These particles, tentatively called bovine leukemia virus (BLV), have a high molecular weight RNA-reverse transcriptase complex and a density of 1.155 g/ml in sucrose solutions. Molecular hybridizations between BLV [3H]cDNA and several viral RNAs show that BLV is not related to Mason-Pfizer monkey virus, simian sarcoma associated virus, feline leukemia virus, or avian myeloblastosis virus. These results were confirmed by hybridization between BLV 70S RNA and [3H]cDNA synthesized in the various viruses tested. The high preference of BLV reverse transcriptase for Mg++as the divalent cation suggests that BLV might be an atypical mammalian leukemogenic ``type C'' virus. DNA · DNA hybridization studies using BLV [3H]cDNA as a probe strongly suggest that the DNA of bovine leukemic cells contains viral sequences that cannot be detected in normal bovine DNA.

Thirty-three epidemiologically unrelated strains of ampicillin-chloramphenicol-resistant isolates of Haemophilus influenzae (22 type b, 11 unencapsulated), isolated over 10 years in Belgium, were compared with 53 ampicillin-resistant chloramphenicol-susceptible isolates (22 type b, 31 unencapsulated). All ampicillin-chloramphenicol-resistant and 76% of ampicillin-resistant chloramphenicol-susceptible strains were resistant to tetracycline, kanamycin, or both. Resistance to these antibiotics was specified by a 37- to 44-MDa conjugative plasmid. The genetic relatedness of these plasmids and of those in multiresistant strains from Spain was investigated. Plasmids specifying ampicillin-chloramphenicol-tetracycline-kanamycin resistance in Belgium or in Spain had highly related restriction fragment patterns. By homoduplex analysis, they had similar molecular organization and contained a structure identical to Tn10-TnCm, a transposon previously identified in chloramphenicol-tetracycline-resistant H. influenzae. Plasmids coding for different resistance phenotypes had less resemblance by restriction endonuclease analysis; however, study of heteroduplex molecules indicated they shared a high proportion of core sequences. These findings support the hypothesis of independent transposition events resulting in resistance plasmids of close molecular organization.

Phosphatase activity (demonstrated by the lead trapping method) occurs mainly in the plasmalemma, mitochondria and tonoplast of maize roots (Zea mays L cv Anjou 18) and is Mg⁺⁺ dependent. Besides, the plasmalemma-bound phosphatase is strongly K⁺ dependent, while the phosphatase activity of the inner cell compartments depends less on K⁺. These results are consistent with the presence of at least two different types of phosphatases in maize roots. The possible function of Mg⁺⁺ and K⁺ in the activation of these enzymes is discussed, as well as the implication of the K⁺-dependent phosphatase in the ion uptake. L'activité phosphatasique (démontrée par la méthode de précipitation du complexe PbPi) se situe essentiellement dans les plasmalemmes, les mitochondries et les tonoplastes des racines de maïs et est dépendante de l'ion Mg⁺⁺. En outre, la phosphatase associée aux plasmalemmes est celle fortement dépendante de l'ion K⁺, alors que celle associée aux organelles cellulaires l'est moins, les résultats confirment l'hypothèse selon laquelle il existerait au moins deux types de phosphatases dans les racines de maïs. Le rôle probable du Mg⁺⁺ et du K⁺ dans l'activation de ces enzymes est discuté ainsi que l'implication de la phosphatase K⁺ dépendante dans l'absorption ionique.

Electron microscopy, immune electron microscopy and complement fixation as methods of detecting rotavirus in the stools of young children with gastroenteritis were compared in a blind study during the winter of 1975-6. Complement fixation was the simplest to perform, was as sensitive as the other two, and allowed a quantitative measurement of viral excretion. Absorption of faecal extracts with fetal calf serum usually removed the anticomplementary activity of faecal extracts.