Recent Papers on CEnothera Mutations. 301 
Species which bear the same qualities in both the male and 
female sex-cells, and whose reciprocal hybrids are therefore alike, 
are designated isogamous ; while species whose functional male and 
female cells are unlike in their latent capacities are called hetero- 
gainous. Thus O. Hookeri, O. Cockerelli and O. strigosa are found 
to be isogamous as is also O. Lamarckiana; while 0. biennis, O. 
biennis Chicago, 0. cruciata and O. muricata are heterogamous. 
In all these cases there is nothing resembling the Mendelian 
recombination of many independent characters, but the various 
hybrids remain constant and uniform in later generations, except 
in an occasional character such as flower-size. The hybrid 
types agree in their main essentials for various crosses, and are 
therefore given names:— rubiennis, conica, gracilis, rigida, etc. 
Thus O. muricata x 0. Hookeri, 0. muricata x O. Cockerelli, 0. 
Hookeri x O. Cockerelli and O. Cockerelli x 0. Hookeri, etc., all 
give the rigida type, differing from each other only in minor 
features. By such parallel series of crosses the character of the 
“Pollenbild” and “ Eizellenbild ” of each species is determined, 
and De Vries calls the process gamolysis. 
Among other cases in which a similar behaviour occurs may be 
mentioned O. Hookeri x O. biennis, which gives an of the 
rubiennis type, the latter splitting in later generations into rubiennis 
and “ Hookeri.” O. biennis Chicago x 0. Hookeri and O. cruciata 
X O. Hookeri give the same result. This is explained by the 
isogamous condition of O. Hookeri and the heterogamy of the other 
three species. In O. Hookeri x O. biennis, e.g., the rubiennis hybrid 
beats in its egg cells only the characters of Hookeri while the 
pollen bears the segregated characters of both parents. Hence the 
type of splitting observed. 
Further, not only these crosses but also the twin hybrids ( Iceta 
and velutina) and the equally extensive series of mutation crosses 
(with the mutants), involving yet a third type of hereditary behaviour, 
are all finally explained and harmonized in connection with the 
theory of mutation. 
De Vries explains not only all this hereditary behaviour but 
also the mutation phenomena in terms of his hypothesis of intra¬ 
cellular pangenesis. Each pangen represents a special character, 
and a pangen may be in (i.) the active, (ii.) the inactive, or (iii.) the 
labile condition, pangens in the labile condition giving rise to 
mutations. A mutation also consists in the passage of a pangen 
from one condition to another, or sometimes in the addition of a 
new pangen. Thus in O. mut. nanella the pangen for stature has 
passed from the active to the inactive condition, in 0. mut. rubrinervis 
this pangen is active, while in 0. Lamarckiana it is in a labile 
condition. Hence Lamarckiana x nanella gives some dwarfs in F, 
while rubrinervis x nanella yields only tails in F t but a varying 
proportion of dwarfs in F 2 . 
I have only touched upon a few of the items in this remarkable 
book, which boldly attempts to explain all the intricate breeding 
behaviour in CEnothera. Though one cannot agree with all its 
statements, yet the lucid explanations given make the work of great 
value to all students of heredity and evolution. 
One other point to which reference may be made is found in 
the recent work of Gates and Miss Nesta Thomas. They have not 
