THE COMPETITION BETWEEN BARLEY AND CERTAIN WEEDS UNDER CONTROLLED CONDITIONS

Chickweed (Stellaria media) is one of the commonest annual weeds on almost all soils, and forms 20–30 % of the weed herbage on the lower greensand soils of Woburn, Beds. It occurs in all crops in this area except on very acid soils.
When barley and chickweed are planted together, with abundance of water and nutrients for both, it is found that increasing the density of planting of the barley reduces the loss due to chickweed competition, but even with very close-planted barley, the loss caused by the weed amounts to nearly two-thirds of the total fresh weight and to four-fifths of the grain yields. This is much greater than with the two annual weeds previously studied (spurrey and mayweed). In a sparse crop of barley, increase in chickweed growth may reduce the barley to less than 10 % of its growth without the weed, while the chickweed itself is relatively little affected by the presence of the barley.
There is no evidence of any specific effect of the roots of the one plant on the other; they intertwine without any sign of attraction or repulsion between them.
Comparisons are made with other annual weeds previously studied, and it is suggested that the method adopted furnishes a means of assessing the relative effectiveness of these weeds in competing with barley.     

The Effect of Subjecting Peas to Air Enriched with Carbon Dioxide: I. THE PATH OF GASEOUS DIFFUSION, THE CONTENT OF CO2 AND THE BUFFERING OF THE TISSUE

The intake of oxygen by an isolated pea was shown to be entirelythrough the micropyle; the loss of CO₂ was about two-thirdsvia the micropyle and the rest through the cuticle. The internalatmosphere of a pea in air contains about 11 per cent CO₂ v/v. Peas transferred from air to CO₂ in air mixtures required nearly24 h for their internal CO₂ content to come to equilibrium.The increase in internal CO₂ content was found to be balancedby a decrease in the content of malic acid and the pH of thetissue changed little. On return to air the changes were reversed.Slices of cotyledons in water apparently maintained their pHby loss of cations rather than change in malate content.     

The impact of defoliating insects on the growth of eucalypt saplings

The effect of spraying insecticide on eucalypt saplings was experimentally tested in a New England woodland. Replicate branches of five species were sprayed fortnightly with Thiodan over a period of 4 months. Their leaf damage, leaf flushes, stem growth, and bud production were compared with those of control branches. Loss of leaf area to insect grazers was extremely variable, ranging from very low levels (e.g. 1.8% for sprayed new leaves of Angophora floribunda) to nearly total defoliation (97.1% for unsprayed new leaves of Eucalyptus viminalis). The sprayed branches consistently suffered less herbivory and grew more than the controls.     

Some Aspects of the Nesting Behavior and Reproductive Biology of Sea Turtles

Basic reproductive data from 21 green turtle (Chelonia mydas),8 leatherback (Dermochelys coriacea), 7 hawksbill (Eretmochelysimbricata), 7 olive ridley (Lepidochelys olivacea),6 loggerhead(Caretta caretta), 1 Kemp's ridley (Lepidochelys kempi), and1 flatback (Chelonia depressa) populations are provided. Someintraspecific and interspecific relationships between size ofnester and clutch, egg size and hatchling size are analyzed.Measurements of reproductive rates (=numbers of hatchlings perfemale per year) in 11 populations varied from 35 to 200 inan olive ridley and loggerhead colony, respectively. Nestingbehavior of each species is described in terms of type of nestingemergence and time spent on the nesting beach (=chelonery).The relatively large number of yolkless eggs laid by many leatherbacksand by some hawksbills invites further study. Some aspects ofsea turtle nesting behavior and reproduction are compared tothose of other chelonians.     

Osmotic and Ionic Regulation of North American Zebra Mussels (Dreissena polymorpha)

SYNOPSIS. Unlike other freshwater bivalves that survive formonths in deionized water, Dreissena polymorpha requires minimalconcentrations of Na, K, Mg, and Cl in the bathing medium forlong-term survival. Although ion transport rates are higherin D. polymorpha compared to other freshwater bivalves, theytend to have lower blood solute concentrations. D. polymorphahas an unusually "leaky" epithelium with a high paracellularpermeability to solutes. Thus, even with high transport rates,it may not be possible for zebra mussels to retain higher bloodsolutes because of the extensive passive loss of ions. Undera hyperosmotic stress, D. polymorpha will rapidly osmoconform(about 12 hr) due primarily to the diffusion of solutes andpartially to the osmotic loss of water. D. polymorpha is notcapable of surviving an imbalance of Na/K in the external medium.In the absence of K the cells will tend to lose volume to achieveisosmotic balance with the blood, but the animals usually diewithin a few days. If D. polymorpha is exposed to excess K inthe environment (1 mM), they will accumulate K in the blood.If the K enters the cells, cellular volume would expand dueto increase in osmolyte concentration, yet, if K remains inthe blood, there will be an electrochemical imbalance. In eithercase, the animal cannot survive much longer than a day. WhenNa and K are present in the medium in a balanced combinationapproximated by artificial seawater (ASW), D. polymorpha willsurvive an acute transfer to 100 mosm ASW indefinitely (months).Our preliminary studies have shown that D. polymorpha will toleratestep-wise acclimation to solutions >250 mosm provided thechanges in salinity do not exceed 50–100 mosm. Freshwaterbivalves, unlike the marine bivalves, have limited free aminoacids in their body fluids and must rely on inorganic ions forosmotic regulation. The free amino acids serve as an importantosmolyte buffer for volume regulation when an animal experiencesan environment of changing salinity. The inability of Dreissena,and perhaps other freshwater bivalves, to tolerate hyperosmoticallyinduced dehydration may be due, in part, to the inability toaccumulate or retain sufficient intracellular K to facilitateregulatory volume adjustments.     

Factors affecting the development of Botrytis cinerea (grey mould) on linseed (Linum usitatissimum) buds, flowers and capsules

A key was produced to describe 10 stages of development of linseed buds, flowers and capsules. Botrytis cinerea conidia germinated more rapidly and germ tubes grew longer on linseed stigmas, petals and mature senescing capsules than on green leaves, sepals and immature capsules. The proportion of conidia which germinated increased and the germ tubes continued growing for longer in the presence of linseed pollen and flower petal extracts. In controlled environment and field experiments, the response of buds, flowers and capsules to inoculation with B. cinerea changed with stage of development; few pre‐flowering buds developed symptoms (brown lesions, then grey mould), but high proportions of flowering and post‐flowering buds did so. Few immature green capsules developed symptoms and the proportion of capsules which developed symptoms increased as they matured. The presence of linseed pollen decreased the incubation period from inoculation with spore suspensions to appearance of B. cinerea symptoms on buds. A disease cycle was produced to suggest the changes in susceptibility of linseed to infection by B. cinerea conidia during bud, flower and capsule development.