PREFACE vii text may be made as clear as possible but also that the student mayacquire some familiarity with the names and contributions of the better known embryologists, both past and present. While most of the copying and redrawing was done by me personally, I am glad to acknowledge the very able assistance I received from a few friends. INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS

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Carbon based nanofillers have shown phenomenal improvements in thermo-mechanical properties of poly vinyl alcohol (PVA) based nanocomposites depending on their interaction with PVA molecules and dispersion in the polymer matrix. In the present study, PVA based nanocomposites with amino-functionalized multi-wall carbon nanotubes (fMWCNTs, 0.2, 0.4, 0.8 and 1.0 wt%) were prepared by a simple casting method from aqueous solution. The relative increase in Young's modulus with 0.4% fMWCNTs was observed to be comparable with that for PVA-nanodiamond composite films which have been shown to have higher strength compared to nanotube and graphene oxide based nanocomposites. In order to investigate the nanolevel molecular packing (sub-nano level free volumes and nano level lamellar structure) and its role in thermal and mechanical properties, positron annihilation spectroscopy and small angle scattering have been used. The crystallinity and morphology of the samples were characterized using X-ray diffraction and scanning electron microscopy. The studies showed that interfacial interaction between PVA molecules and functionalities on the surface of fMWCNTs results in the formation of an ordered structure of PVA molecules which enhances load transfer between the PVA matrix and fMWCNTs leading to improved mechanical properties. The thermal properties of the composites were observed to be unaffected at the studied filler concentration.

With 17 figures in the text)T HE chief features in the development of the angiosperm embryo sac were already known towards the end of the last century, but there is a good deal of confusion with regard to the terminology of the various stages, and it is therefore considered advisable to introduce this essay with a brief account of the normal course of development.A cell in the hypodermal layer of the nucellus becomes specially prominent, and directly or after cutting off a waU cell functions as the megaspore mother cell or embryo-sac mother cell. The first division gives rise to a dyad; the two cells composing it may be called dyad cells but not megaspores, since reduction division is not yet over. The next division results in the formation of a tetrad; each of the four tetrad cells is a megaspore or macrospore. Only the chalazal megaspore grows further and is called the fimctiomng megaspore or primary embryo-sac cell. The two nuclei formed after the first division soon move apart to the poles and will be referred to as "primary micropylar" and "primary chalazal" nucleus respectively. The second division gives rise to a pair of nuclei at each end and the third to two quartets which form the egg apparatus, three antipodal cells and two polar nuclei. The latter fuse to form a secondary nucleus.T he majority of angiosperms investigated so far correspond to the type described above; many deviations have nevertheless been reported and different systems have been devised to classify them ' The term "fusion nucleus" recommended by Coulter & Chamberlain (1903) has the disadvantage that it has also been used to denote the primary endosperm nucleus, which is formed only after triple fusion. PHYT. XXXVI. 5 ^^

The phenol-formaldehyde-carbon nanotube composites were characterized for their free volume properties and interfacial interactions between nanotubes and the polymer matrix. The base polymeric material was a novolac type phenol-formaldehyde (PF) condensation resin cross-linked with para-toluene sulfonic acid. Multi-wall carbon nanotubes (MWCNTs) were synthesized using a catalytical chemical vapor deposition method and characterized using high-resolution transmission electron microscopy. The PF resin-carbon nanotubes composites having 2, 5, 10 and 20% (w/w%) MWCNTs were prepared. The crystallinity and morphology of the samples were characterized using X-ray diffraction and scanning electron microscopy. The free volume size in the polymer nanocomposites was observed to increase with the increase in nanotube content. Positron age momentum correlation (AMOC) studies revealed the electronic environment around different positron annihilation sites. The studies showed that ortho-positronium principally annihilates from interfacial regions of polymer and nanotubes in the nanocomposite. The positron lifetime studies together with AMOC measurements indicate an increase in the free volumes at the interface of polymer and MWCNTs in the composite. The free positron intensities showed that the polymer and nanotubes are weakly interacting in this system.