K.—BOTANYs 171 
7 Dr. Lotsy’s theory that new species originate by Mendelian segre- 
_ gation, if true, would have the advantage that it would make quite 
_ plain the meaning of sexual reproduction. Hitherto there has been a 
good deal of doubt; some authorities have held that sexual reproduction 
stimulated, others that it checked variation. But, if we eliminate varia- 
tion, and rely solely on the products of crossing, we get a clear view— 
_ ‘species, as well as indivduals, have two parents’; sexual reproduc- 
tion can alone provide adequate material for new forms, and can pro- 
_ yide it in unbounded variety. 
“Again, though Dr. Lotsy himself is far from sanguine on this point, 
the crossing theory might be helpful to the evolutionary morphologist, 
- for breeding is open to unlimited experiment, and we might hope to 
learn what kinds of change in organisms are to be expected. For 
example, the Lychnis experiment shows how easily a petaloid race 
may become apetalous. Such results might ultimately be a great help 
in unravelling the course of evolution in the past. We should gain 
an idea of the transformations which might actually have taken place, 
excluding those which were out of the question. At present all 
speculation on the nature of past changes is in the air, for variation 
itself is only an hypothesis, and we have to decide, quite arbitrarily, 
what kind of variations we think may probably have occurred in the 
‘course of descent. One need only recall the various theories of the 
origin of the seed from the megasporangium to realise how arbitrary 
such speculations are. 
But, while recognising certain advantages in the theory of the origin 
of species by crossing, it is not for me to pronounce any opinion as 
fo its truth. It is only the present position of the question that con- 
cerns us to-day. We shall hope to hear a statement of Dr. Lotsy’s views 
from his own lips. 
Some modern geneticists believe that there is evidence for mutation 
_ by the loss of factors, apart from the effects of crossing. Dr. Lotsy con- 
siders that such changes, if proved, can afford no explanation of pro- 
gressive evolution. ‘ Evolution by a process of repeated losses is 
inconceivable.’ It has, however, been pointed out by Dr. Agnes Arber, 
in her recent admirable book on Water-plants, that, on any theory of 
evolution, ‘ what organisms have gained in specialisation they have lost 
in plasticity.’ She avails herself of a human analogy and says: ‘ The 
‘man, though superior to the baby in actual achievement, is inferior to 
it in the qualities which may be summed up in the word ‘‘ promise,”’ 
just as the Angiosperm, though its degree of differentiation so greatly 
_ exceeds that of the primordial protoplasmic speck, is inferior to it when 
eae by its power to produce descendants of widely varying types ' 
(p. 335). 
_ ‘This is true, but it is not clear that this admitted loss of poten- 
tialities is the same thing as the loss of factors, in the sense of genetics. 
For example, if a glabrous variety of Violet really arose as a mutation 
by loss of the factor for hairiness, assuming that such a loss was 
aoa the effect would seem to be a diminution of specialisation, 
though, no doubt, it might also be interpreted as a loss of potentiality. 
b Turning for a moment to Darwin’s own theory of the origin of 
t 02 
g 
—_ 
4 
