102 



P. F. YEO 



The time taken by meiosis is evidently less than the interval between the opening 

 of the flowers, and thus one is not bound to find meiosis in a particular spike, even if 

 it has not occurred in that spike for the last time. In addition, therefore, to selecting 

 spikes of the kind described, an adequate quantity must be collected. The same fact 

 also makes obtaining counts a time-consuming process, though the chance of getting a 

 count is increased by the fact that the two pairs of anthers of each flower are at different 

 stages, and also that various stages are sometimes found in the same anther. 



(3) Fixing 



Buds were fixed in acetic acid and ethyl alcohol, mixed in the proportions 1 : 3, or 

 more usually, in acetic acid, alcohol, and chloroform in the proportions 1:3:4. In the 

 case of wild plants, buds were fixed either at the end of a day's collecting, the plants 

 having been kept in the vasculum, or as soon as the gathering was complete, or they 

 were cut off the plants in situ. The last method was always used for cultivated plants. 



(4) Storage 



Fixed material was preserved in a refrigerator at about — 15°C., as described by 

 Davies (1952). The oldest material used had been stored in this way for six or seven 

 months. 



(5) Staining and Mounting 



The acetocarmine squash method was used, iron alum or iron acetate being used 

 as a mordant. For permanent preparations triacetin was used. A drop is placed at the 

 edge of the coverglass and as the acetic acid of the stain evaporates the triacetin takes 

 its place. This is relatively involatile and allows the preparation to be studied at leisure 

 without it drying up, while the removal of the carmine eliminates the danger of the cyto- 

 plasm becoming stained. After the removal of excess triacetin the coverglass is ringed 

 with " Euparal ". 



Chromosome Counts 



These are based on any stage of meiosis at which the chromosomes could be counted. 

 In Euphrasia prophase does not yield satisfactory counts, though at late diakinesis counts 

 can occasionally be obtained. Metaphase and early anaphase of the first division yield 

 counts most easily. In tetraploids (n=22) the later stages can rarely be counted reliably; 

 of these, late anaphase of the first division (anaphase I) is the most likely to give a count. 

 In diploids (n=ll), however, late anaphase I, metaphase II, and anaphase II can frequently 

 be counted without difficulty. 



There was not time to work on all the material available, and species on which no 

 counts had been made previously (in particular British endemics) were given preference. 



All the plants were determined by the writer. In some cases the fixed specimens 

 were kept separate from others in the same gathering, and these are either in the writer's 

 herbarium, or at the Department of Botany, University College of Leicester. Where the 

 fixed individuals were not separated, the gathering concerned is represented in both these 

 herbaria, and a number are also at the Cambridge Botany School. 



(1) E. micrantha Reichb. Wild material fixed at Withypool, S. Somerset, in 

 August 1952 proved to have finished meiosis. Seeds from this locality (specimen No. 

 E185A) were grown in 1953, but too few spikes were fixed. As a result no meiotic 

 metaphases were obtained, but diakinesis was observed which, though not quite unambi- 

 guous, can be interpreted as showing 22 bivalents. 



(2) E. scotica Wettst. Material from Lawers, Mid Perth (E261) shows n=22. 



