282 REPORT OF THE CONFERENCE ON GENETICS. 
from a state of latency to one of full activity, or conversely may be lowered 
and suppressed.* 
Cross-breeding also promises to give evidence as to the phylogenetic 
relations of two given forms based upon the behaviour of the differen- 
tiating characters in their transmission. The efforts of the earlier experi- 
menters to determine questions of specific identity or distinctness in this 
way are well known. Similar distinctions have been made between racial 
or Mendelising characters (with the so-called “ bisexual ”’ inheritance) and 
specific characters (with so-called “ unisexual”’ inheritance, according to 
Macfarlane) in the way which de Vries has elaborated in his treatise. I 
shall here only add the following conclusions from my own observations : 
Not merely hybrids of various cultivated races, but also those made. 
between cultivated and the wild or putative ancestral forms, such as I 
have bred on a large scale in the case of cereals; e.g. Secale cereale x 
S. montanwm and reciprocal, Hordeum spontaneum x cultivated barleys, 
wheats x /gilops and reciprocal, follow Mendelian laws—a fact which is 
probably an indication that these cultivated forms f arose by discontinuous 
and not by continuous variation from the wild form, followed by a process 
of selection.t 
The Mendelian system has, moreover, proved to hold good, not only 
for what are called organic characters, but also for so-called adaptative 
characters, e.g. for the length of the vegetative period. Thus, a cross 
between winter and summer rye gave a uniform intermediate first genera- 
tion, with a tendency towards the summer type. When the first and 
second generations were grown in summer the following ratio appeared, 
the count being made when the stems began to shoot up: 2°5 summer 
type (shooting) : 1 winter type (resting), and a count made on harvesting 
gave 45:1. The average, therefore, was 3:1: 1. 
A winter cultivation of the first generation and a summer cultivation 
of the second gave an increased proportion of the winter type, and the 
ratio reached 1°98: 1. It mattered far more whether the second genera- 
tion was raised in summer or in winter. When the order was winter, 
winter, summer, the typical split-forms of the third generation gave 
the ratio 1 shooting : 10°5 resting. Summer, winter, summer gave 
similarly 1 : 9°49, and summer, summer, summer gave 3'4 : 1. The 
adaptative character “length of vegetative period’’ shows, therefore, 
clear indication of progressive susceptibility to the influence of external 
conditions, as shown by the changes in the Mendelian ratios. 
* Cp. my paper in Zts. f. das Landw. Versw. in Oesterr. 1904. 
+ By way of comparison with the Mendelian behaviour of cultivated races of the 
same species, I have not only made crosses between cultivated races and wild species, 
but I have also begun experiments with two wild races of the same species, e.g. 
Anagallis arvensis x ce@rulea. 
{ My crosses instituted among the Horde (which are especially suitable for cross- 
breeding) contribute, among others, to a decision of these questions of systematic 
relationship. Crosses between continuous variants, e.g. in the several degrees of 
purple pigmentation in the pods, do not, according to my experience, show any 
Mendelian behaviour. I have repeatedly and expressly emphasised the distinction 
between the non-Mendelian continuously varying characters and the Mendelian dis- | 
continuously yarying characters (Zts. f. das Landw. Versuchsw. in Oesterr. 1901, 
pp. 652-654 ; ibid. 1902, pp. 795 and 847; ibid. 1902, p. 23; Beitr. z. Bot. 
Centralbl. 1903, p. 17). The proviso must now be added that the bearing of 
Johannsen’s principle of “ pure lines” upon this thesis is not clear, pending a 
thorough investigation of the modes of variation of the lines. 
