34 THE ORCHID REVIEW. (FEBRUARY, 1916. 
The cross should be followed up, and if we were asked to name a suit- 
able second parent we would suggest something with a good shape and as 
little green as possible. The more white in the dorsal sepal the better, 
because it implies a reduced amount of green. Size we should regard as 
an altogether secondary consideration, for quality should be the first point 
aimed at. A great deal depends upon the selection of a good second 
parent, and the term means one possessing characters that experience has 
shown to be likely to give at least an approximation to the qualities 
desired. Promiscuous crossing is now completely out of date, and judicious 
selection should be exercised at every stage. Work on such lines will 
certainly be rewarded with success, and undesirable reversions can easily 
be discarded. 
‘“‘Mendelism up to date” is the title of an article in the last issue of 
The Journal of Heredity. It is a review of a new work on “‘ The Mechanism 
of Mendelian Heredity,” by Prof. T. H. Morgan, of Columbia University, 
and his associates. ‘‘One of the useful functions of the volume,” we are 
told, “‘ should be to bring home to readers who have a little knowledge of 
genetics a realisation of the fact that the term ‘ Mendelism’ is nowadays 
used to cover a number of distinct and, in their details, often irreconcilable 
views. . . To put the matter very frankly . . . a large part of the 
so-called ‘ Mendelism’ which is current at present is in some way out of 
date. The first fundamental principle of Mendelism,” it is remarked, “ is 
the existence of relatively constant units, the Mendelian unit-factors, as 
the basis for transmission of all the traits that go to make up an animal or 
plant.” Each of these factors is considered to be nearly or quite constant ; 
to be uncontaminated by other factors with which it may come in contact 
in the cell; and to undergo little, if any, change from generation to 
generation. 
It would take too long to summarise the article, and we may therefore 
give what is termed the “ main features of the mechanism of Mendelian 
heredity, as understood by the authors ” :— 
“1, That the various characters which make up the physical constitution 
of any individual plant or animal are due to the action (concurrently with the 
environment, of course) of what we term, for convenience, factors, separable 
hypothetical units in the germ plasm, capable of independent transmission. 
‘‘2. That each visible character is due to the co-operative action of. 
an indefinitely large number of factors (for such a simple creature as the 
fly, Drysophila, there may be ten or twenty millions); conversely, that 
each of these factors affects an indefinitely large number of characters. 
“3. That these factors, or their material bases, are passed from one 
