144 
R. Ruggles Gates. 
For example, each time lata appears as a mutation from lamarckiana 
the change involved must be the same. Again, in the sense in 
which the term originated, CE. biennsis lata, lamarckiana lata and 
suaveolens lata are all parallel forms. Going farther afield the 
cruciata forms from lamarckiana and biennis, if independent in 
origin, are obviously parallel, but a number of wild species (shortly 
to be considered) which are unrelated to each other .have cruciate 
flowers as a specific character. Some of these may have a common 
descent from a cruciate ancestor, others have almost certainly 
originated independently as parallel mutations. Nor is it certain that 
the change involved is always the same. The Drosophila work has 
shown that two mutations may be so closely alike as to be scarcely 
distinguishable, and yet have different relations in the germ-plasm. 
The conception of parallelism is perhaps even more fertile 
when applied to the comparison of variations in different genera. 
A cruciate mutation has appeared in Epilobium and a similar 
variation probably occurs in other genera. Again, the phenomenon 
of doubling in flowers, to be considered later, shows that doubling 
may occur as parallel mutations in wild as well as cultivated species 
of many families. The same of course is true of white varieties, 
which almost any species of flowering plant may produce. 
Laciniation of leaves, maximum anthocyanin development, nanism, 
lack of chlorophyll (though such a condition may arise from various 
genetic causes), doubling, and a number of other characters may be 
looked upon as probably at any rate parallel mutations. Thus (E. 
rubricalyx and the copper beech may be parallel in that they 
involve in their origin the same kind of germinal change. But this 
cannot be assumed with safety until it has been proved by breeding 
experiments with each. Thus some forms of flower-doubling are 
dominant and some recessive, and white varieties may originate in 
a number of ways. The same is true of gigantism. The gigas 
mutations from four species of CEnothera (Table II) show exactly 
the same peculiarities of stoutness, increase of cell size, 4-angled 
pollen grains and tetraploid chromosomes, so that the change is 
obviously the same in all cases. But in other genera gigantism may 
occur with or without tetraploidy. This whole subject will be 
considered further in connection with the variations of wild species 
of plants and animals. 
