What is Happening 
wide-spread occurrence of hybridism; 
and in conclusion I think we must face 
the fact that among the Crataegi at 
least extreme variability is linked with 
to the Hawthorns ? 279 
extensive hybridization and the con- 
sequent multiplication of species, rather 
than with mutation and the problem of 
the saltatory origin of species.* 
’ The material for this study was collected at the Arnold Arboretum, and I wish to express 
my thanks to Prof. C. S. Sargent for this courtesy. 
I am also indebted to Prof. E. C. Jeffrey, 
in whose laboratory this study was made, for the use of his apparatus as well as for his advice 
and criticism. 
LITERATURE CITED 
1. Brown, H. K.: “The Genus Crataegus and Some Theories of the Origin of Species.” 
Bulletin of the Torrey Botanical Club, 1910. 
2. Jeffrey, E. C.: “Some Fundamental Morphological Objections to the Mutation Theory 
of De Vries.’””’ American Naturalist, 1915. 
3. De Vries, Hugo: “Species and Varieties, Their Origin by Mutation.”’ 
Also: 
4. Bartlett, H. H.: “The Experimental Study of Genetic Relationship.”’ 
of Botany, March, 1915. 
(Lecture IX.) 
American Journal 
5. Henry, A.: Lecture before Royal Dublin Society. March 6, 1914. 
6. Jeffrey, E. C.: “Spore Conditions in Hybrids and the Mutation Hypothesis of De Vries.”’ 
Botanical Gazette, October, 1914. 
7. Jeffrey, E. C.: “The Mutation Myth.” 
Science, 1915. 
The Relation of Vigor to Heredity 
VIGOR AND HEREDITY, by J. Lewis Bonhote. 
London, Adlard & Son and West Newman, 1915. 
Geneticists have been so carried away 
with the idea that characters are 
unchangeable that some of them have 
given little study to the modifying 
effects of outside influences on the ex- 
pression of inherited traits. Mr. Bon- 
hote thinks they have made a funda- 
mental mistake, and asserts that not 
only is the expression of a Mendelian 
character—its dominance or lack of 
dominance, for example—largely de- 
pendent on vigor, but that new varia- 
tions arise from that cause. Further- 
more, he believes vigor to be inherited, 
Pp. 264, illus., price 10s. 6d. net. 
and has carried on breeding experiments 
to demonstrate it. His method of 
measuring an animal’s vigor by its 
color is not the most accurate con- 
ceivable, but he draws some _ highly 
interesting generalizations from his ex- 
periments and from extended observa- 
tions on species in the wild. His 
controlled evidence is limited in extent 
and great weight cannot be placed on 
it, but the book is at least highly 
suggestive and ought to lead to a 
broader view of heredity than is now 
held by many experimental biologists. 
An Elementary Text-Book on Evolution 
EVOLUTION, HEREDITY AND EUGENICS, by John Merle Coulter, professor of Botany 
in the University of Chicago. 
Coulter, publisher, Bloomington, IIl., 1916. 
“The thinking of today that is most 
significant is thinking in terms of 
evolution. Intelligent interpretation of 
life depends upon it,” says Professor 
Coulter)" Yet ib 4s a. fact. that the 
‘average citizen’ has but the vaguest 
ideas of what evolution is.’ He has 
therefore undertaken to give definite 
Pp. 133, illus., price 50 cents. 
School Science Series No. 5, John 
ideas in a little book adapted for use 
by high school and college classes in 
elementary biology. The great extent 
of ground to be covered necessarily 
involves a summary and dogmatic 
method of treatment. The four pages 
allotted to eugenics are particularly 
inadequate. 
