MARCH, Igo9.] THE ORCHID REVIEW. 69 
EPIDENDRUM x KEWENSE: A MENDELIAN EXPERIMENT- 
ANOTHER of the self-fertilised seedlings of Epidendrum x kewense is now 
in flower, and shows partial reversion to the original E. evectum parent. 
The first came true (p. 13),and the second showed partial reversion to E. 
xanthinum (p. 37). Flowers of the reversionary forms, with such of the 
original parents as were available, were exhibited at a meeting of the 
‘Scientific Committee of the R.H.S. held on February 23rd, the others being 
E. X kewense, E. evectum, and a secondary hybrid obtained between them. 
Flowers of E. xanthinum and of the secondary hybrid between it and E. 
X kewense were not available. 
The object of the three experiments has already been explained, and I 
believe they are the first attempted among Orchids with a view of testing 
what is termed Mendelian Inheritance. The result was predicted in advance 
from a Mendelian standpoint, and on the assumption that the colour- 
bearers represent a Mendelian pair, namely that 25 per cent. of the 
seedlings should have purple flowers, like E. evectum, 25 per cent. yellow, like 
E. xanthinum, and the remaining 50 per cent. salmon-colour like E xX 
kewense, without intermediates. The full results can only be given when all 
the seedlings have flowered, but there are already intermediates, in fact 
there are indications of the same variability and dissociation of parental or 
specific character that has been observed ever since the first batch of 
secondary hybrids flowered, and a few suggestions as to the probable cause 
may now be attempted. 
The basis of the Mendelian hypothesis, as I understand it, is the 
conception that the ultimate character-bearers of an organism are fixed or 
constant, and are handed on to their offspring pure or unmodified, though 
entering into new combinations between themselves during the sexual 
process—hence the term “ unit-characters.” The question of ‘* Dominance” 
is of secondary importance. Such a definition at once invites questions. 
Wuat Is A UNIT-CHARACTER ? 
and what is its placein the economy of the organism? Are unit-characters 
the machinery by which the great work of evolution is carried on? or, 
conversely, the restraining influence by which stability of specific character 
is attained? I once suggested to an ardent Mendelian, “ What you term 
unit-characters can only be stages or stopping places on the evolutionary 
journey,” and he replied, ‘‘{ grant you that,” but we got no nearer toa 
solution of the great mystery. Perhaps if we return to somewhat nearer the 
original starting point we shall be able to get a better view of the significance 
of the facts of this complex problem. 
In the simplest and most primitive plants the sexual process is unknown. 
They have not yet arrived at this evolutionary stage. They are unicellular, 
