The Relationship between an Epiphyllous Liverwort and Host Leaves

An investigation was carried out into certain aspects of thestructural and physiological relationships between an epiphyllousliverwort, Radula flaccida Lbg. et G., and a variety of hostleaves. Initial attachment of the epiphylla to the host leafis aided by an adhesive secretion from the rhizoids of the epiphylla.Some rhizoids subsequently penetrate the leaf cuticle and intrudebetween epidermal cells. Penetration results in the death ofsome epidermal cells and rhizoids enter also through the gapsthus created. The presence of well-established epiphyllous colonies was closelyassociated with increased loss of water from leaves by evaporation.Leaves mechanically stripped of their epiphyllae showed a similarlyhigh rate of water loss. It was shown that water and dissolvedradioactive phosphate (salts) can pass from host leaf tissuesinto the epiphylla. It is concluded that, in traditional terminology, epiphyllousR.flaccida is a semi-parasite rather than a simple epiphyte.Some other aspects of the relationship are discussed.     

Further Investigations into the Physiological Relationship Between an Epiphyllous Liverwort and its Host Leaves

Experiments were carried out to investigate the physiologicalrelationship between an epiphyllous liverwort, Radula flaccidaLbg. et G., and its host leaves. The osmotic potential of theepiphylla cell sap (-30 to -35 bar) was found to be much lowerthan that of the host cells (-10 to -12 bar). There is thereforea good physiological basis for the movement of water from thehost leaves to the epiphylla. The amount of light incident onthe host leaf which is intercepted by even the heaviest epiphyllacolony investigated was less than 2 per cent and this was foundto produce no measurable difference between the chlorophyllcontents of epiphylla-colonized and uncolonized parts of thehost leaf. ¹⁴CO₂ light fixation products were found not to movebetween the host leaf and the epiphylla in either direction.It is concluded that the dependence (parasitism) of R.flaccidaon its host leaves is partial and does not include the derivationof organic food substances.     

The Vegetative Growth of Helianthus annuus and Phaseolus vulgaris as Affected by Seasonal Factors in Freetown, Sierra Leone

Sand-culture experiments were carried out in full daylight atsuccessive weekly intervals between March and December 1969,to investigate the effects of seasonal changes in climatic factorson the growth of Helianthus annuus and Phaseolus vulgaris inFreetown. Values for a number of growth parameters were calculatedfrom the dry weights of the leaves, stems, and roots, and fromthe leaf areas. Simultaneously the diurnal changes in climaticfactors were recorded. Multiple regressions linking light, temperature, and relativehumidity with some of the growth parameters were calculated.The total variance accounted for in the regressions of relativegrowth-rate, net assimilation rate, and leaf weight ratio onlight, temperature, and relative humidity ranged from 51 to60 per cent in P. vulgaris. In H. annuus relative humidity wasless important; the percentage proportion of total varianceaccounted for in the regression of leaf weight ratio (and leafarea ratio in both species) on light and temperature was notsignificant. The results showed that H. annuus grew faster than P. vulgaris,but the latter's growth was depressed less by the dull weatherof the rainy season. The relative growth-rates of both specieswere positively dependent on light and temperature while theirnet assimilation rates were negatively dependent on relativehumidity, and their leaf area ratios negatively dependent onlight. All parameters used except leaf area ratio and leaf areato leaf weight ratio showed seasonal variations correspondingto dry and rainy seasons. The initial and final values of leafarea ratio and weight ratios were always different but did notvary in the same direction in both species. The results are discussed in relation to similar work done elsewhere.