REVIEWS. 
161 
Mutations in Horticulture— The question of mutations in horticulture 
possess added interest from the fact that Darwin’s theory of natural 
selection was, to a large extent, based upon the experience of breeders. 
In natural selection we have selection of species within a genus, and selec¬ 
tion within the species. So in horticulture there are analogous practices 
called respectively race-breeding and variety-testing. Careful examina¬ 
tion of horticultural facts and practice leads to the conclusion, “ that really 
progressive mutations have hardly been observed in horticulture. Hence 
the theoretical value of the facts is far less than might have been ex¬ 
pected.” 
Systematic Atavism. —The reversion of a species to the form of some 
ally from which it is supposed to have descended by the loss of one or 
more characters is termed systematic atavism. A study of systematic 
atavism shows that the loss of characters is only apparent and that they 
are present, though latent, even when not outwardly manifest. When in 
cases of atavism they return to activity, they do so suddenly “ and not 
by a slow and gradual recovery of the former features.” The assertion 
is supported that “ the visible elementary characters are essentially an 
external display of qualities carried by the bearers of heredity, and that 
these bearers are separate entities, which may be mingled together, but 
are not fused into a chaotic primitive life substance.” Systematic atavism 
thus emphasizes the importance of the conception of the so-called unit 
characters. These facts are emphasized by studies of species of Primula, 
Androsace, Anthurium, Zea Mays, tomatoes, and other plants. 
“ Latency, from this point of view, must be one of the most common 
things in nature. All organisms are to be considered as internally formed 
of a host of units, partly active and partly inactive. Extremely minute 
and almost inconceivably numerous, these units must have their material 
representatives within the most intimate parts of the cells.” 
Taxonomic Anomalies. —Characters which are specific in one case often 
arise as anomalies or as varieties in other instances. They are then 
termed taxonomic anomalies, e. g., the heaths are considered as one of 
the lowest gamopetalous plants, but among them Labrador tea {Ledum), 
Indian pipe {Monotropa) , and wintergreen {Pyrola) are polypetalous. 
“ Such cases of atavism make it probable that the coherence of petals has 
originally arisen by the same method, but by action in the opposite direc¬ 
tion. Proof of this conclusion is found in the accidental gamopetals of 
such polypetalous forms as poppy, Saponaria, Clematis, Peltaria, and Si- 
lene. Taxonomic anomalies are also found in leaves. In all cases, “the 
idea of a slow evolution on the ground of utility is absolutely excluded. 
No other explanation remains than that of sudden mutation, and once 
granted for the abnormal cases, this explanation must obviously likewise 
be granted for the analogous specific characters. 
“ Our whole discussion shows that mutations, once observed in definite 
instances, afford the most probable basis for the explanation of specific 
characters at large.” 
