13S Prof. H. Marshall Ward. Effect of Mineral [Nov. 4, 



backwards through the history of our planet, we probably come to a 

 time when the rigidity was so small that the stable configuration of 

 equilibrium would be unsymmetrical. At this time the earth would 

 be pear-shaped, and the transition to the present approximately 

 spherical form would take place through a series of ruptures. It is 

 suggested that the earth, in spite of this series of ruptures, still retains 

 traces of a pear-shaped configuration. Such a configuration would possess 

 a single axis of symmetry, and this, it is suggested, is an axis which 

 meets the earth's surface somewhere in the neighbourhood of England 

 (or possibly some hundreds of miles to the south-west of England). 

 Starting from England, we find that England is at the centre of a 

 hemisphere which is practically all land : this would be the blunt end 

 of our pear. Bounding the hemisphere we have a great circle of which 

 England is the pole, and it is over this circle that earthquakes and 

 volcanoes are of most frequent occurrence. Now, if we suppose our 

 pear contracting to a spherical shape, we notice that it would probably 

 be in the neighbourhood of its equator that the changes in curvature 

 and the relative displacements would be greatest, and hence we should 

 -expect to find earthquakes and volcanoes in greatest numbers near to 

 this circle. Passing still further from England we come to a great 

 region of deep seas — the Pacific, South Atlantic, and Indian oceans : 

 these may mark the place where the "waist" of the pear occurred. 

 Lastly, we come almost at the antipodes of England to the Aus- 

 tralian continent : this may mark the remains of the stalk-end of 

 the pear. 



" Experiments on the Effect of Mineral Starvation on the Para- 

 sitism of the Uredine Fungus, Paccinia dispersa, on species of 

 Bromus" By H. Marshall Ward, Sc.D., F.R.S., Professor of 

 Botany in the University of Cambridge, Pieceived Novem- 

 ber 4— Eead November 27, 1902. 



I have shown in previous publications that the parasitic Uredine 

 Puccinia dispersa, growing on grasses of the genus Bromus, is usually 

 very closely adapted to the species of host-plant selected: that 

 although no morphological differences can be detected between the 

 fungus as met with on different species of Bromus — A, B, C, &c. — it by 

 no means follows that spores from the parasite, as found growing on A, 

 will infect B or C, or that spores from the fungus as reared on B or C 

 will infect the species A. 



On the whole, it has so far appeared probable that the fungus 

 growing on a given species — e.g., B. mollis — infects most readily those 



