392 SECTIONAL TRANSACTIONS.— K. 



groups of upright threads whose interweaving re-establishes the macro- 

 scopic summer form. There has thus been demonstrated a microscopic 

 phase which may serve to maintain the existence of the species during the 

 winter and at the same time represent the alternate haploid gametophytic 

 phase of the life cycle. 



The results of culture experiments have been confirmed by careful col- 

 lection of material in the open field throughout one complete year. Stages 

 corresponding to those obtained in cultures have been obtained from the 

 localities where the summer form of the plants is normally distributed. 



Dr. E. AsHBY. — The physiology of hybrid vigour in maize. 



The aim of the experiments was to find a physiological interpretation of 

 hybrid vigour in certain strains of maize. Populations of inbred lines, 

 their reciprocal Fj crosses, the Fg and the F3 generations were grown, and 

 the relative rates of increase in dry weight or wet weight followed through 

 the grand period of growth. 



The Fi hybrids in every instance showed hybrid vigour, and were there- 

 fore heavier than their parents. They did not, however, show any increase 

 in relative growth rate, or efficiency index. The efficiency indices were, in 

 fact, inherited from one parent, the higher efficiency index being dominant. 

 In the F2 and F3 populations there was less hybrid vigour and the efficiency 

 index segregated out. 



Hybrid vigour was not due to increased efficiency index ; but was found 

 to be nothing more than the maintenance of an initial advantage in embryo 

 weight of the hybrids. 



Reciprocal Fj crosses exhibited different degrees of hybrid vigour, though 

 they had the same efficiency indices. This too is due to an initial difference 

 in their embryo sizes. 



Dr. N. L. Penston. — Some aspects of potassium distribution in plants. 



Dr. T. Whitehead. — On the respiration of healthy and leaf-roll potatoes. 



Infection with the virus of leaf-roll has no direct effect on the respiration, 

 in oxygen or in nitrogen, of potatoes at any stage in the life-cycle. Immature 

 tubers, whether healthy or diseased, respire at a higher rate than do mature 

 tubers after storage. After sprouting, the rate rises rapidly to a maximum 

 in the young plant and falls gradually with tuber formation. 



In comparing the respiration of healthy and leaf-roll plants at each stage 

 it was found that the diseased immature tubers show a higher rate than 

 comparable healthy ones, but this falls to the same, or slightly lower, level 

 in mature tubers before sprouting. Whilst still in the sprouting stage the 

 healthy plant shows the higher rate but, with the unfolding of the leaves, the 

 rate of respiration of the diseased plant quickly exceeds that of the healthy 

 and remains higher when tuber formation has begun. When, however, very 

 young plants are allowed to assimilate, the healthy plant respires at a higher 

 rate than the diseased until the latter accumulates a definite excess of carbo- 

 hydrates in the leaves, after which the diseased plant again respires at the 

 higher rate. 



It is suggested that these differences can be correlated with the failure of 

 autolysis in the infected seed-tuber, and the accumulation of excessive 

 amounts of translocatory carbohydrates in the diseased foliage. 



