Stomatal Responses to Humidity and the Water Potentials of Epidermal and Mesophyll Tissue

Effects of ambient humidity on relative water contents (RWC)and water potentials were measured separately for epidermaland mesophyll tissues in leaves of two species. Water potentialsdid not always change in the same direction as RWC within thesame tissue and rarely were the changes in water potential andRWC of one tissue correlated with those of the other. The natureof the humidity responses of stomata in certain species is discussedin relation to these results and to the anatomical propertiesof epidermal tissues.     

Phase shifting the circadian rhythms of nocturnal insects by temperature changes

The behavioural rhythms of three species of nocturnal insects were studied: locomotion in a cockroach, luminescence in a firefly and luminescence in a glow-worm. The behaviour was released at the change from light to dark in all cases. In continuous dim light, a circadian rhythm was apparent with a period of from 22.5 to 27 h in the cockroach, and from 19 to 23.5 h in the glow-worm. In constant dim light, the cockroach shifted the phase of its rhythm when subjected to a change of temperature. A temperature step down some time prior to the expected onset of locomotion generated a phase advance, whereas a temperature step up generated a phase delay; the greater the step up, the greater the phase delay. By advancing the change from light to dark, it was found that glow-worms could synchronize immediately to advances of up to about 6 h only. At greater advances an increasing phase angle difference between onsets of darkness and activity occurred. However, if a temperature step down was applied at the light change, immediate synchronization occurred up to 9–12 h before the normal onset. A theory is propounded which assumes that the onset of rhythmic behaviour is determined by the interaction of a circadian process of sensitization and a threshold for release of the behaviour. The threshold is high at high temperatures and light intensities, and low at low values of these. A temperature step up raises the threshold and delays the activity while a step down lowers the threshold and advances the activity.     

Quondam Gill-Covers

On the basis of its positional relations to the neuromast and branchial-arch systems, a greater part of the cephalic exoskeleton in teleostome fishes is suggested to have evolved from dermal elements which once provided support for gill-covers. More precisely, the following results are arrived at: parts of the decking of the ethmoid region of the endocranium stem from the branchiostegic exoskeleton of the terminal, or first, branchial unit; the external cheek-plates are made up of modified branchiostegic components of the premandibular (second), mandibular (third), and hyoid (fourth) branchial units; the lower jaws include inferior branchiostegic elements of the mandibular and hyoid branchial units; those branchiostegic elements of the hyoid branchial unit which remained free of the external cheek-plates and the lower jaws gave origin to the exoskeletal support of the hyoidean opercula as well as to the two rows of submandibular bones.     

Pressure and Solute Potentials in Stomatal Cells of Tradescantia virginiana

The postulated mechanical advantage of subsidiary cells overguard cells has been estimated using leaves of Tradescantiavirginiana. The turgor pressures of subsidiary cells were adjusted to bezero or maximal by plasmolytic treatments, and the resultingstomatal apertures were measured. The ‘mechanical advantage’was calculated from two mathematical models which define itas an ‘antagonism ratio’. The discussion deals withmethods of preparing the tissue, the validity of the plasmolytictreatments, and the function of the antagonism ratio in relationto the Spannungsphase     

Functional Epidermal Cells are Necessary for Abscisic Acid Effects on Guard Cells

Experimental results are presented which show that abscisicacid (ABA) causes stomatal closure only if the stomatal complexis adjacent to live epidermal cells. It is further shown thatABA acts by affecting solute fluxes into and out of epidermaland guard cells. Live epidermal cells function as recipientsfor solutes and thereby assist their movement out of the guardcells. ABA-mediated solute leakage from guard cells alone doesnot suffice to cause stomatal closure within one hour.     

Teratology and Early Fish Development

SYNOPSIS. The developing teleost embryo is a highly complexand balanced physico-chemical system in equilibrium with itsenvironment. Even slight alterations of the external aquaticenvironment, or a pathochemical modification of the immediatematernal environment, may lead to developmental modifications.Multiple malformations produced as a result of metabolism ofteratogens and interacting factors are similar to syndromesobtained by hybridization. Modifying factors, although possessingsome specificity as to intracellular targets are nonspecificas to the types of anomalies produced in most instances. Embryonic responses to teratogens occur at various developmentalstages and at different levels of organization, modifying thenormal development. Intracellular molecular syntheses and sensitivemetabolic targets essential for normal development may be blockedor modified, and rates of differentiation and growth affected.Embryo-sensitivity and resistance is related to tolerance leveland regulatory capacity. The terata observed have been correlatedwith molecular mechanisms and disorganization with disruptionsof cellular contacts and translocatory yolk cytoplasmic movements. Causality as it pertains to early teleost aberrant developmentis reviewed, and suggestions for research and an extensive bibliographyof the relevant literature provided.     

Morphologie und Morphogenese des Bodenciliaten Oxytricha granulifera sp.n. (CiIiophora, Oxytrichidae)

Oxytricha granulifera sp.n. differs from other members of the genus by its subpellicular granules and the strongly shortened dorsal kinety 4. The overall pattern of the morphogenetic events is similar to that known from other Oxytrichidae. However, the oral primordium evolves de novo between the left marginal cirral row and the postoral cirri. The six anlagen of the frontoventral cirri are of different origin. Two anlagen of the proter evolve from parental frontal cirri, two from the opisthe, and one includes basal bodies of the proter and opisthe. Two anlagen of the opisthe evolve from the oral primordium, and three primordia originate from the postoral cirri. Frontal cirrus 1 evolves from the paroral membrane in the proter, and from the oral primordium and the anlagen of the frontoventral cirri in the opisthe. The genus Oxytricha can be subdivided into several groups with regard to the origin of its oral primordium and the development of the frontoventral cirri. The morphogenesis of the dorsal kineties in the Hypotrichida is reviewed. Seven different modes of origin are distinguished. We conclude that morphogenetic features cannot be used in the classification of the Hypotrichida at the generic level, because we have too little information to decide whether special morphogenetic features are important at the generic or species level.