Granite Inselbergs Research Articles

An Ecological Study of Vellozia Schnitzleinia, a Drought-Enduring Plant of Northern Nigeria

Over 60 years ago, Kearney & Shantz (1911) suggested a grouping of plants of arid regions which is still useful: (1) drought escaping; (2) drought evading; and (3) drought enduring. They elaborated these categories as composed of: (1) those plants with a brief growth cycle; (2) those plants able to restrict water loss or with very extensive root systems serving for water uptake; and (3) those plants able to survive even when water uptake cannot take place. The last group includes many of the cacti and some other succulents, leafless and non-succulent desert shrubs, and certain grasses and sedges. One sedge, Afrotrilepis pilosa (Boeck.) J. Raynal, common in West Africa and colonizing granite inselbergs, has been studied by Hambler (1961). He reported that leaves of this sedge can survive even when as much as 86% of their total water content has been lost. Within 24 h of watering intact desiccated plants, the brown and brittle leaves turn yellow and then green and flexible. Eventually the plants return to normal appearance and presumably to normal metabolic activity. Field observations in northern Nigeria suggest as remarkable 'resurrecting' (group 3) ability in another monocotyledonous plant-Vellozia schnitzleinia (Hochst.) Martelli var. occidentalis Milne-Redh. This paper reports initial observations and experiments on ecological aspects of the water relations of this plant.

A Poikilohydrous, Poikilochlorophyllous Angiosperm from Africa

THE sedge, Trilepis pilosa Boekl, a primary colonizer of rock surfaces on granitic inselbergs in West Africa, has been found to possess the property, most unusual in an angiosperm, of becoming dormant by losing most of its intracellular water during the dry season, with subsequent recovery on moistening. Plants with this property are found mainly among the lower groups (bacteria, fungi, algae, lichens and bryophytes); the word ‘poikilohydrous’ being first used by Walter1 in this connexion. Some pteridophytes also exhibit this property: for example, Iljin2 described drying out and recovery of the fern Notochlaena marantae R.Br., and I have found Selaginella njam-njamensis Hieron., which colonizes thin soil mats on West African inselbergs, and the epiphytic fern Platycerium stemaria (P. Beauv.) Desv., which is sometimes epiphytic on Trilepis, to be poikilohydrous.

"Abnormal" Shore Platforms

Conditions in New Zealand are especially favorable to the study of shoreline forms, and, probably for this reason, New Zealand geologists are impressed with the frequency with which subhorizontal benches are developed near high-water level on rocky, retrograded coasts, and, whatever individual beliefs may be held as to their origin, discussions have made it obvious that local geologists are strongly of the opinion that such benches are a far commoner feature than the literature would lead one to expect. The present paper aims at briefly discussing shore platforms which make a distinct departure from the profile which has been described as the "normal shore profile," or the "profile of equilibrium," and for this reason only has the term "abnormal" been applied to them in the title of this paper. The writer firmly believes that such platforms are in no respect truly abnormal, but that characteristically they are expectable, and therefore the normal products of shoreline erosion, and is assured by correspondence that his is no isolated belief. Ten years ago the writer published a brief paper on certain rock platforms which are a prominent and characteristic feature of shoreline topography in many harbors of North Auckland, and of which an outstanding example is afforded by the well-known "Old Hat" near Russell in the Bay of Islands, New Zealand.' As with most other North Auckland harbors, the Bay of Islands has been formed by the submergence of a maturely sculptured land-mass, and the Old Hat, which is illustrated in Figure i, represents an emergent