416 BOTANICAL GAZETTE [MAY 
The supposed initial mutations of our strain, therefore, must 
have produced half mutants, the gametes of which split in every 
generation into about equal parts of potential grandiflora with the 
lethal factor, and into viable ochracea. The fecundation must then 
produce one-fourth of germs of grandiflora with the double lethal 
factor and thereby doomed to die off within the seed; one-fourth 
of viable but weak ochracea, which will be constant in their progeny; 
and one-half of hybrids between the two mutants, in which the 
qualities of the type of the species will be dominant, whereas the 
lethal factor must be recessive. 
Among the living seedlings the proportion of green hybrid 
_ mutants and yellowish ochracea must therefore be 2:1, and the 
average figure for the latter was 26 per cent, although this was 
* somewhat too low on account of the loss of part of the yellow seed- 
lings in early youth. Artificial crosses between the hybrid mutants 
and the ochracea should give about 50 per cent of either type. I 
found for both the reciprocal crosses about 34 per cent, but the 
figure was depressed from the same cause. A repetition of these 
experiments, excluding the influence of these losses, is proposed; 
it is expected to give a fuller proof. 
We assume the supposed initial mutations to have been analo- 
gous to the mutations into lorea and gigas, which may still be 
observed to occur in my garden. New mutations into ochracea may 
occur also, but they must evidently always escape observation, 
being different in no respect from the secondary or mass mutation. 
BARTLETT has pointed out the analogy between the phenomenon 
of mass mutation and Mendelian splitting, observing, however (1, 
p. 452), that ‘‘there can be no doubt that mass mutation is not Men- 
delian segregation, although the two phenomena have points of 
resemblance.” In our instance this resemblance is plain enough, 
but a splitting is called Mendelian if it is observed among the pro- 
geny of hybrids between different species, varieties, or strains, 
whereas the half mutants are hybrids between mutated and non- 
mutated sexual cells of the same parent. They are produced by one 
experimental pure line, whereas real hybrids are the result of the 
combination’ of different strains. The hybrid mutants start from 
a mutation; they can never be made use of as an argument against 
