524 
R. RUGGLES GATES AND NESTA THOMAS. 
It lias thus been shown that tetraploidj is a condition which 
may, and probably always does, arise suddenly in Nature; 
and the appearance of tetraploidy as it occurs in man}" plants 
and animals is thus shown to be a progressive evolutionary 
process of considerable interest. 
The present paper is concerned with another change in 
chromosome number obviously of a different character, 
namely, the occurrence of 15 chromosomes in (E. mut. lata 
and its relatives. Miss Lutz (1912) has recently examined 
the root-tips of twenty-eight lata plants and reports in every 
case 15 chromosomes, and one of us (Gates, 1912b) in a 
study of the megaspore mother-cells and nucellus of a lata 
plant, found the number of chromosomes also to be 15. The 
investigations here described were begun to determine 
whether this number was constantly associated with the lata 
characters, and what numbers were to be found in related 
forms such as G1 . mut. semilata; also what chromosome 
numbers were present in mutants with lata-like foliage which 
occurred in other species, e. g. ffi. biennis L., and certain 
hybrid races (03. mut. rubricalyx x CE. gran di flora 
Solander), which will be referred to later. 
For this purpose a cytological examination of many plants 
fi-om various sources has been made, the material for study 
having been collected in all cases from plants in our own 
pedigree cultures. These plants were grown at the John 
Innes Horticultural Institution in 1912, and we are indebted 
to Prof. Wm. Bateson, F.R.S., for the facilities afforded. 
Methods. 
The flower-buds were all collected between July 31st and 
August 20th, 1912, buds of all ages being fixed. The fixing 
fluids used were 1 per cent, chrom-acetic acid, weak Flemming 
and Hermann’s solution. The chrom-acetic fixation was found 
to be most suitable for this material and this type of investi- 
gation in which the number and morphology of the chromo- 
somes was the main concern. The microtome sections were 
