64 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
most needed. This can only be got by an exhaustive study of the results 
of cross-breeding between various forms whose, common origin is not 
very distant. Such experiments must, besides, be repeated sufficiently 
often to give a fairly extensive series of abservations on which to base 
conclusions. Anyone, therefore, who wishes to work on these lines would 
do well to restrict himself to an examination of the transmitting pro- 
perties of a small group of closely allied varieties or species, and to explore 
these properties thoroughly within that group. 
Cross-breeding, then, is a method of investigating particular cases of 
evolution one by one, and determining which variations are discon- 
tinuous and which are not, which characters are capable of blending to 
produce a mean form and which are not. It has sometimes been urged 
as an objection against this method of investigation that the results are 
often conflicting. It has been said that such work will only lead to 
accumulations of contradictory evidence. It is, however, in this very 
fact of the variety of results that the great promise of the method lies. 
When varieties and species are tested by this method it is found that 
their mutual relations are by no means alike, and properties are disclosed 
which can in no other way be revealed. 
In illustration, I will refer to three cases of hairy and smooth varieties. 
In each case there is a well-marked discontinuity between the two 
varieties ; but, as is shown by the evidence obtained by cross-breeding, 
the nature of the relationship* of the two forms to each other is different 
in each case, and the distinctness is maintained by different means. 
The plants (produced at the meeting) illustrating the following 
observations were raised by Miss E. R. Saunders, of Newnham College, 
Cambridge, who is carrying out a large series of experiments on this 
subject. 
The first case is that of MJatthiola incana, a hoary species, and its 
smooth variety known in gardens as the Wallflower-leaved Stock. Ex- 
periments in crossing these two forms were made by Trevor Clarke, and 
briefly described by him in ‘“ Report of Botanical Congress,” 1866. 
Amongst other things his investigations showed that on crossing these 
two varieties the offspring consisted entirely of completely hoary and 
completely glabrous individuals, no intermediate being present. Miss 
Saunders’s work entirely confirms thisresult. The type-form used by her 
was procured from seed of presumably wild specimens growing in the 
Isle of Wight. The glabrous variety was the ordinary garden form the 
origin of which is not known to us. In this case discontinuity is 
manifested in its simplest form. 
The second example is that of Lychnis diuwrna. There, again, the 
normal is hairy. A glabrous variety was found by Professor de Vries, 
and was by him crossed with the type. All the first generation of cross- 
breds inherited the hairiness in its complete form. When, however, these 
plants were crossed again with the smooth form, the result was a mixed 
progeny, of which some were hairy and others smooth. The same result 
*The term “relationship” is somewhat misleading, but I cannot find a better. 
It is used to denote not simply the blood-relationship of the forms to each other, but 
those physiological relations subsisting between them which are manifested by 
experimental crossing. The word is thus used in a sense similar to that which it 
bears when we speak of the chemical relations of one substance to another. 
