Vol. 3 Issue 1

A. Mahmoud, A.M. EI·Sheikh and S. Abdul Baset
Anastatica hierochuntica is an annual plant which is widely distributed in Saudi Arabia and is associated with habitats where runoff water collects. The seeds of A. hierochuntica do not have genetically fixed innate dormancy to offset the possibility of population extinction owing to complete germination followed by complete mortality under desert conditions. However, laboratory and field experiments showed that the regulation of germination by hydration of the woody persistent pods of the indurated fruiting plant links germination to the time when abundant water is available and restricts the distribution of the species to habitats which normally receive abundant runoff water so that successful subsequent seedling establishment is possible. Dissemination is delayed until adequate moisture is available during the rainy season. The wide amplitude of A. hierochuntica with regard to its germination temperature responses, coupled with the synchronization of germination with the season of optimal conditions, contribute to its success and wide distribution in Saudi Arabia. The salt tolerance of A. hierochuntica is affected by temperature. When moisture and temperature conditions are favourable, its seeds are capable of germination in salinities greater than those encountered by, and tolerated by, the adult plants.

Shaukat A. Chaudhary
Sixteen taxa of Heliotropium (Boraginaceae) in Saudi Arabia are described. They are: H. aegyptiacum Lehm., H. arbainese Fres., two subspecies of H. bacciferum Forssk., H. bottae Defl., H. crispum Desf., H. curassavicum L., H. digynum (Forssk.) Asch. ex C. Christ., H. europaeum L., H. longiflorum (Hochst & Steud ex. DC.) Jaub. & Spach, H. ovalifolium Forssk., H. pterocarpum (Hochst & Steud ex. DC.) Jaub. & Spach, H. strigosum Willd., H. subulatum (DC.) Vatke, H. sp. A and H. sp. B. Four other species which may be present in Saudi Arabia are discussed

A. Mabmoud
Hammada elegans is a desert perennial, widely distributed in Saudi Arabia and an effective sand-binder. Germination was tested over a range of fluctuating temperatures and in various concentrations of seawater under two fluctuating temperature regimes. The wide range of temperatures at which seeds on H. elegans can germinate, their high salt tolerance, the synchronization of fruit-setting with optimal conditions for seed germination and subsequent seedling establishment and the massive production of light winged fruits providing effective means of dispersal, all contribute to the success and wide distribution of H. elegans in Saudi Arabia.

Loutfy Boulos
The Asir Mountains, in the SW of Saudi Arabia, have a rich and varied flora still inadequately known. The author was able, in May 1980, to collect in an area to the south of Abha, 266 species of vascular plants in 59 families are listed from his collections; some are reported as new for Saudi Arabia or the Arabian Peninsula; 98 of these species are not recorded in Migahid, Flora of Saudi Arabia, 2nd ed., 1978.

D.A. Al-Sammerrai and M.M. Barbooti
Thermogravimetric analysis under inert atmosphere has been applied as a unique method of studying lubricating greases of various compositions. While this quick method of analysis proved useful in distinguishing between lubricating greases, it also provided significant information on the relative composition of these products.

Keith J. Fisher, Mosunmola G. George-Taylor and Ayodeji B. Iginla
Infrared studies of the interaction of acetyl-, carboxaldehyde- and benzoyl- ferrocenes with phenols have shown that the acid base interaction, measured both as the change in O-H stretching and the C=O stretching frequency, are related to the Hammett constant of the phenol. The change in O-H and C=O stretching frequencies are not necessarily linearly related when the groups attached to C=O are significantly different in mass.

S.B. Salama and S. Wasif
Free energies and enthalpies of formation of the weak complexes SO2X-, SOCl2X-, SOBr2X- and SO2Cl2X- (X= Cl, Br, I) in the mixed solvent acetonitrile-dimethyl sulphoxide (MeCN-dmso) can be described by the existence of solute-solvent and solvent-solvent interactions. Stability constants of dmso or MeCN with the sulphur compounds SO2, SOCl2, SOBr2 and SO2Cl2 are evidence to solute-solvent interactions. Solvent-solvent interactions are confirmed from H(vap), S(vap) and H(vis) of the mixtures of MeCN and dmso. They are supplemented by the excess functions from refractive index, dielectric constants and densities of solvent mixtures. Infrared and Raman shifts point to the formation of 1:1 MeCN-dmso adducts.

F.H. Mosalamy, S.A.S. El-Hemaly, M.G. Abd El Wahed and H. El-Didamony
This study deals with the hydration kinetics of tricalcium aluminate in the presence of one mole CaO in excess than the stoichiometric composition of ettringite as well as of monosulphate hydrate. It is not yet known whether or not the calcium hydroxide controls the formation of ettringite during the hydration of commercial portland cement. Two mixes from C3A, CaO and CaSO4 were prepared having the molar ratios of 1:1:3 and 1:1:1 respectively. The hydration products as well as the hydration kinetics were studied using the X-ray diffractometry and differential thermogravimetry techniques

A. Mahmoud, A.M. El-Sheikh, M.M. Youssef and M. El Tom
The littoral salt marsh vegetation at Al-Magawah, near Ras Sheikh Humeid on the Gulf of Aqaba, Saudi Arabia, is characterized by its zonal arrangement. The Arthrocnemum glaucum zone is followed successively landward by the Suaeda pruinosa, Nitraria retusa and Zygophyllum coccineum zones. Inundation, the dynamic process of accretion, differences in ground level, distance from the shore, vertical elevation above the saline water table, salinity gradient, soil texture and aridity all contribute to the pattern of distribution, structure and composition of the vegetation.

A.M. El-Sheikh, A. Mahmoud and M. El-Tom
The vegetation in the inland salt marsh at Al-Shiggah, in Al-Qassim district is characterized by its zonation. The different community types which characterize this vegetation are: Seidlitzia rosmarinus, Suaeda pruinosa, S. pruinosa- Salsola baryosma- Zygophyllum decumbens, Z. decumbens, and Hammada elegans. Differences in ground level, vertical elevation above the saline water table, moisture and salinity gradients and climatic aridity all contribute to the pattern of distribution, structure and composition of the vegetation.