Ocrorer, 1908.] THE ORCHID REVIEW. 291 
be a blend, or the hybrid may assume the character of the prepotent parent. 
Ontogeny is a mnemic phenomenon, and evolution in the modern sense is a 
change in the ontogenic rhythm. If the rhythm is fixed no new variations 
can arise, so that we may ask how the rhythm may be altered. A beech 
tree may be made to develop different forms of leaves by exposing it to 
sunshine or to shade. The ontogeny is different in the two cases, and what 
is specially interesting is that there exist shade-loving plants in which a 
structure similar to that of the shaded beech leaf is typical of the species. 
And Goebel has pointed out that in some Orchids the assimilating roots 
take on a flattened form when exposed to sunlight, but in others this 
morphological change has become automatic, and occurs even in darkness. 
The mnemic theory depends on the possibility of what is known as 
somatic inheritance, or the inheritance of acquired characters, which some 
deny in toto, but which it is forgotten, may be, as he had tried to show, an 
integral part of all evolutionary development. Weismannism, though now 
much modified and liberalised, in his opinion failed to bea satisfactory theory 
of evolution, for in spite of its apparent strength it fails to connect the 
process of ontogeny with physiological processes of which we have any 
definite knowledge. After discussing other phases of the question, which 
we cannot go into, and pointing out difficulties and objections, Mr. Darwin 
expressed the opinion that somatic inheritance lies at the root of all 
evolution. 
We may fix our eyes on phylogeny and regard the living world as a great 
chain of forms, each of which has learnt something of which its predecessors 
were ignorant; or we may attend rather to ontogeny, where the lessons 
learned become in part automatic. But we must remember that the distinc- 
ition between phylogeny and ontogeny is an artificial one, and that routine 
and acquisition are blended in life. The great engine of natural selection is 
taunted nowadays, as it was fifty years ago, with being merely a negative 
‘power, but he ventured to think that the mnemic hypothesis of evolution 
made the positive value of natural selection more obvious. If evolution is a 
process of drilling organisms into habits, the elimination of those that can- 
not learn is an integral part of the process, and is no less real because it is 
carried out by a self-acting system. Natural selection attains in a blind, 
mechanical way the ends gained by a human breeder; and may be said to 
have the power of an automatic master, with endless patience and all time 
at his disposal. 
This is necessarily a very brief summary of a most interesting and im- 
portant address, and its bearing upon the progressive development of Orchids, 
and indeed of the evolution of the Order, will be obvious to many Of our 
readers. 
