io8 
L. Cockayne 
tion.” Hybridism, a known cause of similar variation, is certainly 
a more scientific explanation than is the bald statement that the 
group is “ variable/’ and yet no cause assigned for such variation, 
except the unproved and unlikely supposition that an organism has 
within itself some factor which can cause it to produce such inter¬ 
mediate offspring. Even, if mutations were taking place far more 
frequently than has ever been suggested, their nature is not con¬ 
sidered that of forms intermediate between distinct groups, their 
distinguishing feature being the possession of one, or more, new 
characters and of breeding true. So in what follows, when in the 
Manual 1 it is stated, that two groups of individuals, to which specific 
rank had previously been assigned, could not be considered species 
because they were connected by intermediates, to me it is good 
evidence that such groups are true species, and the intermediates 
between them hybrids! And, in nearly every instance this opinion 
has been supported by field-observations. 
Darwin in The Origin of Species makes a distinction between 
“mongrels” (crosses between varieties) and “hybrids” (crosses be¬ 
tween species), but he considered that, except in the matter of 
fertility (mongrels being usually fertile), there was “the closest 
general resemblance” (sixth edition, p. 247) between them. Re¬ 
garding this matter of fertility Darwin had animals chiefly in mind 
and was comparing the domestic with the feral. But, in the case of 
plants, the matter is different for, as every -gardener knows, there 
are hundreds of self-fertile hybrids, and some breed true. 
As for the species and varieties of floras generally no distinction 
can be drawn between them, for what is considered a variety one 
day may be acknowledged as a species the next and vice versa. Nor, 
in the light of present-day knowledge, can any distinction be made. 
There is the aggregate species—a quite arbitrary group—its content 
being a matter of opinion and not of natural law. The true-breeding 
groups of individuals (the “jordanons” of Lotsy, l.c. p. 27) are the 
realities , the aggregate species is merely a convenient abstraction 2, . 
When there is a group of individuals not too closely related to any 
other group it is placed by itself and may be termed an “invariable 
1 T. F. Cheeseman, The Manual of the New Zealand Flora, Wellington, 
1906. Throughout this paper cited as Manual . A new edition is being prepared 
by Mr Cheeseman. 
2 For a recent discussion of the species question see L. Diels, l.c. pp. 161-65; 
also Lotsy, l.c. pp. 13-28. For the full reasons for my views on the subject 
see A Consideration of the Terms “ Species” and “Variety” as used in Botany, 
with Special Reference to the Flora of New Zealand, Trans. N.Z.Inst. 49 , 
pp. 66-79, 1917. 
