SUMMARYThe chromosome numbers and external morphology of Mimulus naturalized in Britain are compared with those of experimentally produced Fi hybrids between Mimulus guttatus DC. and M. luteus L.

SUMMARYA growth analysis of plants raised under controlled environment conditions was used to examine the response to temperature of five contrasting tomato cultivars bred for outdoor production. Curves were fitted to the data of dry weight and leaf area and, to compensate for ontogenetic drift, instantaneous values of growth analysis parameters were calculated from these curves at a specific growth stage. Differences in relative growth rate which could be exploited in a breeding programme were not detected, though there were large differences in the components of relative growth rate. These were, however, compensatory within a cultivar. It was concluded that in order to select a genotype with improved growth rate it would be necessary to disrupt the compensation mechanism between the components of relative growth rate.

Summary Samples of populations of Dactylis smithii native to Madeira were collected for studying seed set and morphological characteristics. The analysed data showed two main groupings, the reasons for these groupings and the resultant classification are discussed.

SUMMARYHybridizations were carried out between samples of ten diploid Dactvlls subspecies. Both pollen fertility and 'fertility index' of hybrids decreased from initial cross to F2. There was no correlation of fertility with geographical distribution of the parents, and despite the fall in hybrid fertility it was considered that gene exchange would not be completely prevented.

No abstract