Gemmules of sponges from a warm lake

1. Two types of gemmules were found, each in a different species of sponge, from the warm monomictic Lake Kinneret: (i) clustered gemmules, sharing the pneumatic layer of the gemmular capsule and resembling gemmules of Eunapius ; (ii) gemmules that develop non-synchronously, containing amphidisc spicules within the gemmular capsule and resembling those of Ephydatia . Algal cells were not detected within either type of gemmule although they exist in the developed sponges.
2. Sponges began producing gemmules in the lake with the onset of lake drawdown and ceased when lake level was minimal. The gemmules hatched when the lake level began to rise.
3. Under experimental conditions gemmules hatched between 13 and 35 °C. Germination was optimal at 20–25 °C. Chilling of young gemmules prior to incubation at 25 °C improved germination rate.
4. The percentage of germinating dry gemmules diminished 4–6 months after their collection from the lake. None germinated after 10 months. Submerged gemmules maintained high viability with ageing (up to 100% germination 18 months after collection). Desiccation influenced gemmule viability over time, by both decreasing the percentage of germinating gemmules and increasing the lag time before onset of germination.
5. Gemmules kept in the dark germinated significantly less than those illuminated for 12 h day     

Cytokinins and Senescence in Lemon Leaves

The effect of leaf age on cytokinin level was studied in Citrus limon (L.) Burm. f. cv. Eureca. It was found that mature 1-year-old leaves and senescing 2-year-old leaves contained considerably more cytokinins than young 3-month-old leaves. No consistent distinct decrease in cytokinin activity was revealed when the leaf passed from the mature to the senescing state. It was concluded that the results cannot be regarded as supporting the hypothesis that leaf senescence is brought about, at least partially, by a decrease in the level of its cytokinins.     

Evidence for Hormonal Regulation of the Selectivity of Ion Uptake by Plant Cells

Kinetin exerted opposing effects on the uptake of K⁺ and of Na⁺ by leaf discs of Helianthus annuus: The absorption of K⁺ was stimulated and that of Na+ was inhibited. The K⁺/Na⁺ ratio in kinetin-treated discs was 80–100 % higher than in control tissue. Kinetin also promoted K⁺ uptake by detached cotyledons which had been removed from light-grown seedlings. On the other hand, no clear effect on the absorption of Na⁺ by these cotyledons could be established. Benzyladenine brought about a significant elevation in the K⁺/Na⁺ ratio in attached cotyledons. It is concluded that cytokinins bring about a change in the selectivity of the cells of sunflower leaves and cotyledons towards K⁺ and Na⁺, such that the ‘affinity’ of the cells for pottasium is increased, as compared to the ‘affinity’ for sodium. The possible significance of such a change in selectivity is discussed.     

Dactylosoma hannesi n. sp. (Dactylosomatidae,Piroplasmia) Found in the Blood of Grey Mullets (Mugilidae) from South Africa1

ABSTRACT. A new species of Dactylosoma (Dactylosomatidae, Piroplasmia), for which the name Dactylosoma hannesi n. sp. is proposed, was discovered in blood erythrocytes of Mugil cephalus, Liza richardsoni, and L. dumerili (Mugilidae) from Swartkops estuary, located east of Port Elizabeth, South Africa. The life cycle of this species differs in some respects from that described for all other known species of Dactylosoma and Babesiosoma. Mature schizonts contain eight nuclei but undergo division only to two to four daughter cells. During cytoplasmic cleavage, schizonts assume triad, rosette, or cruciform shapes. Merozoites are finally produced through a series of binary fissions of these daughter cells which may also be involved in additional nuclear divisions.     

On the Relation Between the Effects of Auxin on Growth, pH and Potassium Transport

The relation between the effects of auxin on growth, pH and potassium transport in hypocotyl segments of Helianthus annuus was studied. In a solution containing 20 mM Na₂SO₄ auxin-induced growth was accompanied by an auxin-induced pH drop in the medium. (NH₄)₂SO₄, at the same concentration, brought about an almost complete abolishment of the effect of auxin on the pH. The magnitude of auxin-induced growth was, however, only slightly reduced. This result does not confirm the hypothesis according to which the action of auxin on growth is a result of its effect on the pH. In a solution containing 2 mM sodium phosphate buffer an inhibitory action of IAA on the release of potassium from the tissue was observed. Addition of 20 mM Na₂SO₄ to the medium brought about a complete abolishment of this effect. The magnitude of auxin induced pH drop was, however, similar in the two treatments. It was concluded that, although under suitable experimental conditions, a close relationship may exist between the effects of auxin on pH on K⁺ transport, the coupling between the two phenomena is not obligatory.     

Visual Cues for Predator Face Recognition by Reef Fishes

A morphometric analysis of 20 different facial features of reef fishes was carried out in order to assess cues which could serve for predator recognition. 105 different species of 35 different families were included in this study. The main features of potential discriminatory value were head width, head shape, the size of the mouth and its shape, the shape of the eyes, their diameter, and the distance between the eyes. Color and pattern were of no potential discriminatory value. Discriminant function analysis showed that two cues, the distance between the eyes and the size of the mouth, were sufficient for good predator recognition. The camouflage of piscivorous cues by predatory fish is discussed. The mimicry of piscivorous cues by some prey fishes as an anti-predator strategy is suggested for two types of false eye spots simulating the frontal aspect of a piscivore.     

A promotive action of kinetin on amylase activity in cotyledons of Phaseolus vulgaris

Kinetin and the embryo axis acted similarly in bringing abouta promotion of amylase activity in cotyledons of Phaseolus vulgaris.No promotive effect of gibberellic acid or indole-3-acetic acidon amylase activity could be detected. It is suggested thatthe regulatory action of the embryo axis on starch degradationin the cotyledons of P. vulgaris is mediated by cytokinins. (Received May 4, 1970; )     

Morphology and Anatomy of Stems and Pedicels of Spring Flush Shoots Associated with Citrus Fruit Set

Flowering and vegetative shoots of ‘Shamouti’ orange[Citrus sinensis (L.) Osbeck] and ‘Marsh’ seedlessgrapefruit (Citrus paradisi Macf.) were examined for correlationof their morphology and anatomy with fruit set. Fruit set isfavoured on leafy inflorescences whereas abortion is nearlycomplete on leafless inflorescences. Leafless inflorescencesof ‘Shamouti’ with one flower were found to havea very thin stem which contained few vascular bundles, whereasthose with three flowers had better-developed vascular systems.The vascular system of leafy inflorescences is significantlydifferent from that of leafless ones and contains a distinctcentral xylem cylinder. The vascular area of leafless inflorescencesis only about one-quarter of that of the leafy ones. The vascularsystem of grapefruit resembles that of the ‘Shamouti’orange. This study emphasizes the importance of the dimensionof the vascular system for fruit set and provides a possibleexplanation for the better fruit set on both leafy and leaflessinflorescences with several flowers compared with single-floweredinflorescences. Anatomy; citrus; fruit set; leafless inflorescence; leafy inflorescence; pedicel; vascular system; vegetative shoot