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The effect of two controlled, contrasting environments on the anatomy and cell wall degradability of leaf laminae was examined in a range of temperate and tropical grass species: Dactylis glomerata cv. S37, Festuca arundinacea cv. S170, Lolium perenne cv. S24, Phleum pratense cv. S48 (temperate); Bothriochloa barbinodis, Cenchrus ciliaris cv. Biloela, Chloris gayana cv. Pioneer and Eragrostis curvula (tropical). Environment I was cool and humid with a low light intensity and adequate water supply; Environment II was hot and dry with a higher light intensity and restricted water supply. Cell walls were isolated from leaf laminae and their degradability determined using a commercial fungal cellulase. The anatomy of the lamina of the eighth leaf on the main stem was examined to determine the possible anatomical basis for differences observed in cell wall degradability. Differences in cell wall degradability were found between species grown in the same environment, but there was no significant difference between the tropical and temperate species when considered as two separate groups. Environment had a significant but opposite effect on the tropical and temperate species: the cell walls of all the tropical grasses were more degradable in Environment II than in I, whereas in the temperate species they were less degradable. It was concluded that the low feeding value of tropical grasses is not caused by an inherently low degradability of cell walls in the leaf laminae, nor by the effects of a hot, dry environment on cell wall degradability. Anatomical features which could have accounted for differences between species in cell wall degradability included variation in the lignification of the parenchyma sheath cells and epidermis and in the size of girders, strands and marginal caps, as seen in transverse section. The increase in cell wall degradability in tropical. species in Environment II was due, at least in part, to an increase in the proportion of sclerenchyma fibres which were degraded by cellulctse. This type of sclerenchyma fibre had very thick walls and was only ii found in the tropical species. The decrease in cell wall degradability in temperate species could be accounted for by an increase in the thickness of lignified cell walls, and an increase in the resistance of epidermal and parenchyma sheath cell walls to degradation.

In this thesis several aspects of the singing behaviour of six European members of the genus Turdus have been studied. It has been-demonstrated that these six species show three distinct types of singing behaviour. They are; 1. Species with small repertoire size and stereotyped song characteristics (ring ousel and redwing). It is suggested that song in these species functions primarily as a territorial 2. Species advertisement. with medium to large repertoire size and stereotyped song characteristics (blackbird and mistle thrush). It is suggested and observations support the contention that one important function for song in these species is territorial. The large repertoire characteristic of individuals of these species indicates that there may also be an important mate attraction component. 3. Species with large to extremely large repertoire size and variable song characteristics (song thrush and, possibly, fieldfare but results are based on measurements from only one recording of one individual). Observations indicate that the song of the song thrush probably functions primarily in mate attraction and it is suggested that song may play a similar role in the fieldfare. It is suggested that in other avian species in which individuals possess large repertoire sizes and sing in a complex or unpredictable manner that song is likely to function primarily in mate attraction. A series of experiments was conducted on individuals of the mistle thrush, blackbird and song thrush. These revealed that individuals of these species use a second kind of singing behaviour in situations simulating territorial intrusion. (Jommon to all species is an increase in sound frequency of song during or following playback of conspecific song. The singing behaviour of three individual song thrushes was studied in an attempt to find rules governing sequencing of song types. The most important point to emerge is that individuals of this species seem to organise their singing behaviour in a hierarchial manner. It is possible to identify groups of song types within which transitions occur more frequently than at random. This is like the singing behaviour of the blackbird and it may be that hierarchical organisation of singing behaviour is a common phenomenon in species in which individuals possess large song repertoires. The functional significance of such behaviour is unclear. Finally, with a view to confirming or refuting Hartshorne's anti-monotony threshold principle, the singing behaviour of the six European species and that of eight others from various faunal regions was studied to see to what extent it conforms with predictions of the principle. Several measures of song continuity and versatility were i applied and it was found that for macro measures (see Chapter 4) there is a very significant relationship between the two parameters. 'Other predictions of Hartshorne were not confirmed. It is suggested that although the principle seems to apply to some aspects of Turdus song its major failing is that it does not provide an explanation for interspecific differences in repertoire size.

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