ALGAE AND BRYOPHYTA 659 
of germs. But at least the existence of post-sexual divisions in certain 
Algae associated more or less definitely with reduction show that the initial 
structure postulated by our theory does actually exist. At the same time, 
the Thallophytes present no facts which directly disprove the hypothesis 
for land-growing plants: they do illustrate, however, other types of cytologi- 
cally distinct generations, both algal and fungal, analogous, no doubt, to 
that seen in the Archegoniatae, but probably produced along phyletic lines 
which were distinct, and subject to quite different external conditions 
during their development. 
A general objection to the whole theory of antithetic alternation was 
raised some years ago on the ground of the assumed improbability that 
new parts should appear in the life history.1 It was pointed out that 
nature is conservative, and it was stated that when a new organ is formed 
it is almost always fashioned out of some pre-existing organ. The adage 
was quoted “ex mihilo nihil fit”: the same objection to the whole anti- 
thetic position has recently been reiterated from the Continent. The reply 
to this general objection is a very simple one: it is, that the zygote from 
which our hypothesis starts is not “nothing”: it is a cell, with all the 
powers and possibilities of a complete—and in point of fact a diploid— 
cell. It has already been concluded generally as regards the sporophyte 
(p. 100) that a living cell which is capable of growth has not a specific 
and unalterable function: this we may conceive to have been the initial 
condition of the zygote and of its early products. The hypothesis involves 
a development of the potentialities of a living cell: the zygote is actually 
seen in each normal ontogenetic cycle to give rise by gradual steps of 
development to the whole sporophyte: the theory contemplates a cognate 
development as having proceeded gradually in the course of descent. In 
face of the ontogenetic facts the initial objection does not appear to be valid. 
Passing to the more special question of the origin of members, it is 
necessary to examine the inherent improbability which is assumed to 
surround their appearance as new structures. It is plain that the difficulty 
lies in their phyletic not in their ontogenetic origin: for it is a fact which 
anyone may observe that in the individual development new parts do 
appear where previously there were none: new axes, new leaves, hairs, 
-emergences, roots, all are originated in this way, each growing out from a 
spot previously in the individual unoccupied. The position, then, of those 
who entertain this objection appears to be that what is the rule in the 
development of the individual is inherently improbable in the evolution of 
the race. This is surely a new principle in morphology. The practice 
of the science has been hitherto to hold the exact converse; the onus 
probandi lies with those who declare that the origin of organs in the 
1Dr, Scott. Presidential Address to Section K (British Association Report, 1896, 
996). The position there taken up was substantially that of Pringsheim (Gesammelte 
Abhand, ii. p. 370). It was criticised in my address to Section K (British Association 
Report, 1898, p. 1032). 
