Tracheary Element Differentiation Induced in Isolated Cylinders of Lettuce Pith: a Bipolar Gradient Technique

To study the influence of morphogenetic gradients on vasculardifferentiation patterns, a new technique was developed whichallows different substances to be applied at opposite ends ofa tissue block. It yielded information on the mobility of particularmorphogens and on the dependence of callus formation and trachearyelement differentiation on their presence. Application of indol-3ylacetic acid (1AA) (10 mg l^–1), zeatin (0.1 mg l^–1)and sucrose (3 per cent, w/v) in various combinations to theends of cylindrical explants of lettuce pith (Lactuca sativaL.) showed that (a) callus formation was stimulated by IAA,whereas induction of tracheary elements required both IAA andzeatin; (b) callus was confined to a few millimetres at theends of the explants, and tracheary elements occurred mainlywithin the callus; (c) sucrose or its metabolic products diffusedthe 10 mm length of the explants, while IAA and zeatin wereeffective only close to the application site; and (d) some callusand tracheary elements formed when no sucrose was applied, butboth increased with sucrose application, though inhibition oftracheary elements formation occurred with high sucrose concentrations. differentiation, pith explant, tissue culture, xylogenesis, indol-3yl acetic acid, sucrose, zeatin, lettuce, Lactuca sativa     

Photosynthesis in Stands of Green Peppers. An Application of Empirical and Mechanistic Models to Controlled-environment Data

The photosynthetic response of stands of green peppers to lightand CO² is examined by means of various mathematical models.Several single leaf response equations are considered, fromthe simple and ubiquitous rectangular hyperbola, to more sophisticatedforms incorporating photorespiration and the oxygen effect.By making the usual assumptions about stand structure and lightpenetration, mechanistic crop response equations arc derivedfor each of the different leaf response equations. First, asa purely empirical approach, the leaf response equations areapplied directly to crop data, and it is concluded that therectangular hyperbola with a term for dark respiration [eqn(2)] gives an adequate summary of crop response to light andCO₂. Second, four mechanistic equations of crop response areapplied to the data, and, although the results are equivocal,it is suggested that the simpler crop equations [eqns (15) and(17)] are satisfactory at the present time, and it is not yetpossible to detect the results of photorespiration and the oxygeneffect directly in the crop data.     

Further Observations on Root Contraction

Further observations, by light and electron microscopy, on theanatomy of root contraction in Hyacinthus orientalis cvs. arereported, together with some comparisons with Narcissus andGladiolus. It is maintained that root contraction in these andsome other species is essentially a growth process, as previousinvestigators have shown, and that an understanding of the re-directedgrowth of the cortical cells which brings it about may be basedon the specialized structural features of their cell walls,here described. Physical, anatomical and comparative reasonsare given for our belief that the alternative explanation ofthe contractile process in Gladiolus which relates it to cellcollapse resulting from transpirational ‘pull’ isuntenable. anatomy, contraction, Hyacinthus, Narcissus, Gladiolus, root     

Elevational trends in butterfly phenology: implications for species responses to climate change

1. Impacts of global change on the distribution, abundance, and phenology of species have been widely documented. In particular, recent climate change has led to widespread changes in animal and plant seasonality, leading to debate about its potential to cause phenological mismatches among interacting taxa. 2. In mountainous regions, populations of many species show pronounced phenological gradients over short geographic distances, presenting the opportunity to test for effects of climate on phenology, independent of variation in confounding factors such as photoperiod. 3. Here we show for 32 butterfly species sampled for five years over a 1700 m gradient (560–2260 m) in a Mediterranean mountain range that, on average, annual flight period is delayed with elevation by 15–22 days per kilometre. Species mainly occurring at low elevations in the region, and to some extent those flying earlier in the year, showed phenological delays of 23–36 days per kilometre, whereas the flight periods of species that occupy high elevations, or fly in late summer, were consistently more synchronised over the elevation gradient. 4. Elevational patterns in phenology appear to reflect a narrowing phenological window of opportunity for larval and adult butterfly activity of high elevation and late‐flying species. 5. Here, we speculate as to the causes of these patterns, and the consequences for our ability to predict species responses to climate change. Our results raise questions about the use of space–time substitutions in predicting phenological responses to climate change, since traits relating to flight period and environmental associations may influence the capacity of species to adapt to changing climates.     

Indications for and results following exploration of the common bile duct for stones

Among 100 consecutive patients who had removal or drainage of the gallbladder and exploration of the common bile duct for stones, there were no serious, immediate or late complications and there were no operative deaths. Ninety-six of the 100 patients had stones in the gallbladder, in the common duct, or in both, and 52 of these patients had one or more stones in the common duct. Ten patients died subsequently of unrelated causes. Six patients were lost to followup. Of the 84 patients whose present condition is known, 75 or 89 per cent have had a completely satisfactory result. Six more patients have minor residual symptoms, and for them the result has been classified as good. In three patients, the results were unsatisfactory. Cholangiograms taken before the removal of the T-tube showed residual stones in two patients. In each instance, the stone or stones have been subsequently passed and both patients are in excellent condition.     

Changes in the Temperature Response of Hill-Reaction Activity of Chilling-Sensitive and Chilling-Resistant Plants after Hardening

The temperature response of Hill-reaction was measured in chloroplastsisolated from mung bean (very chill-sensitive), two tomato cultivars(less chill-sensitive) and pea (chill-resistant). Computer analysisof the plots of log rate against reciprocal of absolute temperatureindicated that in each case, they were composed of three straightlines, meeting at characteristic break temperatures. Neitherthe activation energies (Ea's¹), calculated from the slopesof the lines, nor the break temperatures correlated with chillingsensitivity. Treatment of the two tomato cultivars at 12 ?Cand either low humidity (effective in reducing sensitivity)or high humidity (relatively ineffective) both caused loweredEa values and increased unsaturation in the chloroplast membranephospholipids. However, this evidence does not, in general,support the idea of any relationship between chloroplast membranefluidity and chilling injury.     

Physical and chemical aspects of Chew Valley and Blagdon Lakes, two eutrophic reservoirs in North Somerset, England

Chew Valley and Blagdon Lakes are two shallow, hard-water, lowland eutrophic reservoirs, situated near Bristol in the south-west of England. Chew Lake is more turbid and richer in plankton but poorer in macrophytes than Blagdon, and is more exposed to wind action. Both lakes show evidence of transient stratification in the summer coupled to deoxygenation of the bottom water, which has led to release of nutrients from the sediments. Severe algal blooms in Chew Lake in 1968 and the consequent filtration difficulties led to the establishment of a collaborative research programme between the University of Bristol and the Bristol Waterworks Company, to define the present biological status of the lakes, and to predict their possible future development. The work covers a wide range of measurements and observations on the limnological conditions of the lakes, which form an elegantly contrasted pair, and this paper describes their general physical and chemical features.     

The metabolism of ingested and injected [3H]ecdysone by final instar larvae of Heliothis armigera

ABSTRACT. When larvae of Heliothis armigera (Hüber) are fed on a diet containing [³H]ecdysone they produce large quantities of ecdysone 22-palmitate, probably in the gut. The radiolabel is excreted in the faeces chiefly as ecdysone 22-palmitate, but appreciable quantities of unchanged ecdysone are also found together with traces of ecdysone 2-and 3-acetates. No polar metabolites are found with ingested ecdysone, and the ecdysone probably did not penetrate the gut wall, since on injection into the body, ecdysone was appreciably converted into polar metabolites.