PI2 
curious organs, Hugo Mohl, who, in a very careful and elaborate 
memoir specially devoted to the somata of Proteacex, has the 
following passage (‘‘ Vermischte Schriften,” p. 248) :—‘‘ Striking 
as is the above-described structure of the stomata in Proteacez, 
we should, nevertheless, not be justified in regarding this as a 
peculiarity of this family ; for all the variations which we meet 
with in the structure of the stomata in Proteaceze are also to be 
found in plants belonging to widely distant orders.” 
From the above considerations, I cannot resist the opinion 
that all presumptive evidence is against European Proteace, 
and that all direct evidence adduced in their favour has. broken 
down upon cross-examination. And however much these Eocene 
leaves may assume a general character, which may be more 
frequent in Australia (in Proteaceze and other orders) than else- 
where, all that this would prove would be, not any genetic affinity 
with Australian races, but some similarity of causes producing 
similarity of adaptive characters. 
Another series of conclusions drawn by paleontologists from 
their recent discoveries, which appears to me to have been carried 
too far, relates to the region where a given species originated. 
The theory that every race (whether species or group of species 
derived from a single one) originated in a single individual, and 
consequently in one spot, from which it has gradually spread, is 
a necessary consequence of the adoption of Darwinian views ; 
and when Mr. R. Brown (‘‘On the Geographical Distribution 
of Conifers,” Trans. Bot. Soc. Edin. x. p. 195) sneers at my 
having qualified it as a perfect delusion, he must have totally 
misunderstood, or rather misread, the passage he refers to in my 
last year’s address. The expression is there specially applied to 
the idea of general centres of creation, whence the whole flora 
of a region has gradually spread, in contradistinction to the 
presumed origin of individual races in a single spot, which is 
there as distinctly admitted. The determination of where that 
spot is for any individual race is a far more complicated question 
than either geographical botanists or palzontologists seem to 
suppose. ‘‘ Every vegetable species,” as well observed by Prof. 
Heer, ‘‘has its separate history,” and requires a very careful 
comparison of all the conclusions deducible as weil from present 
distribution as from ancient remains. The very important fact 
that Zaxodium distichum, Sequoie, Magnolia, Salisburia, &c., 
existed in Spitzberg in Miocene times, so satisfactorily proved by 
Heer, shows that the vegetation of that country then comprised 
species and genera now characteristic of North America ; but it 
appears to me that the only conclusion to be drawn (independently 
of climate and geology) is, that the area of these species and 
genera had extended continuously from the one country to the 
other, either at some one time or during successive periods. The 
proposition that “ Spitsberg appears to have been the focus of 
distribution of Zaxodium distichum,” because an accidental pre- 
servation of its remains shows that it existed there in the Lower 
Miocene period, would require at least to be in some measure 
confirmed by a knowledge of the flora of the same and preceding 
periods over the remainder of its present area, the greater part 
of which flora is however totally annihilated and for ever con- 
cealed from us. The fact that Pizzs abies existed in Spitsberg in 
Miocene times, and that no trace of it has been found in the 
abundant Tertiary remains of Central Europe, is very instructive. 
It might show that that tree was of more recent introduction into 
the latter than the former country ; but it cannot prove that it 
was not still earlier in some other region, whence it may have 
spread successively into both territories, still less that its course 
of dissemination was directly from Spitsberg over Northern and 
Central Europe. Moreover, the determination of zs adies is 
not so convincing as that of the Zaxodium, resting as it does, 
if I correctly understand Prof. Heer’s expression, on detached 
seeds and leaves, with a few scales of one cone, and may require 
further confirmation. 
In the above observations it is very far from my wish to de- 
tract from the great value of Professor Heer’s researches. In- 
terested as I have been in the investigation of the history of 
races of plants, I have deeply felt my general ignorance of 
paleontology, and consequent want of means of checking any 
conclusions I may have drawn from present vegetation by any 
knowledge of that which preceded it, and the impossibility at 
my time of life of entering into any detailed course of study 
of fossils. Like many other recent botanists, I am obliged to 
avail myself of the general results of the labours of palaeonto- 
logists, and if I have here ventured on a few criticisms, it 
is only as a justification of the hope that they may in some 
measure distinguish proved facts from vague guesses, in order 
NATURE 
| Fune 9, 1870 
that we may know how far reliance is to be placed on their 
conclusions. 
Spontaneous generation, or Heterogeny, is a question which 
continues to excite much interest. It has been the subject of 
detailed memoirs, of violent controversies, and of popular articles 
in this country, and still more on the Continent ; but the solution 
of the problems still involved in doubt does not seem to me to 
have much advanced since I alluded to the opposing theories of 
Pasteur and Pouchet in my Address of 1863. The present state 
of the case appears to me to be this: in the higher orders of 
animals every individual is known to proceed from a similar 
parent after sexual pairing; in most plants, and some of the 
lower animals, besides the result of that sexual pairing which 
they all are endowed with, reproduction from the parent may 
take place by the separation of buds, by division, or sometimes 
by parthenogenesis ; in some of the lower Cryptogams, the first 
stage in which the new beings are separated from the parent is 
that of spores termed agamic, from the belief that they never 
require previous sexual pairing, although the range of these 
agamic races is being gradually restricted, a remarkable advance 
having been recently made in this direction by Pringsheim in 
his paper on the pairing of the Zoospores in Pandorina and 
Eudorina. In all the above cases, in all organised beings which 
in their earlier stages are appreciable through our instruments, 
every individual has been proved to have proceeded in some 
stage or another from a similarly organised parent. But there 
are cases where living beings, Vibrios, Bacteria, &c., first ap- 
pear under the microscope in a fully formed state, in decaying 
organic substances in which no presence of a parent could be 
detected or supposed: three different theories have been put 
forward to account for their presence: first, that they are suddenly 
created out of nothing, or out of purely inorganic elements, which 
is perhaps the true meaning disguised under the name of spon- 
taneous generation, a theory not susceptible of argument, and 
therefore rejected by most naturalists as absurd; secondly, that 
they are the result of the transformation of the particles of the 
organic substances in which they are found, without any action 
of parent Vibrios or Bacteria; and this appears to be what is 
specially termed Heterogeny ; thirdly, that there existed in these 
organic substances germs which had proceeded from parent 
Vibrios and Bacterias, but too minute for optical appreciation, and 
that their generation was therefore normal. The supporters of 
Heterogeny rely on the impossibility of accounting for the appear- 
ance of the Vibrios and Bacterias in any other manner; for 
they say that although you treat the medium by heat in a her- 
metically closed vessel in such a manner as to destroy all germs 
and intercept ail access, still these beings appear. This their 
opponents deny, if the experiments are conducted with proper 
care. So it was seven years ago, and so it is still, although the 
experiments have been frequently repeated in this country, in 
France, and in North America, almost always with varying 
results. All reasoning by analogy is still in favour of reproduc- 
tion from a parent; but Heterogeny has of late acquired partisans, 
especially in Germany, among those who are prepared to break 
down the barriers which separate living beings from inorganic 
bodies. 
Brown’s celebrated theory of the Gymnospermy of Conifers and 
allied orders has been of late the subject of keen controversy. 
Objected to by Baillon, Parlatore, and others, it had been strongly 
supported by Caspary, Eichler, and lastly, by Hooker in his im- 
portant Memoir on Welzwitschia, published in our Transactions 
in 1863. There the question seemed to rest till last year, when 
two detailed papers appeared, the one contesting, the other ad- 
vocating the theory. The most elaborate is without doubt that 
of Gustav Sperk, in the ‘‘ Memoirs of the Imperial Academy of 
Sciences at St. Petersburg.” He gives a very fair vésumed of all 
that had been published on the subject, and proceeds to record 
in detail his own observations on the structure and anatomy of 
the flower in a considerable number of Conifers, of Zphedra 
alata, Gnetum latifolium, and two species of Cycas, illustrated by 
well-executed analytical figures. He endeavours to prove, chiefly 
by their anatomy and development; that the coating which en- 
closes the nucleus is carpellary, not ovular, of independent origin, 
always free, and often earlier developed than the nucleus—that 
what is wanting in gymnosperms is not the ovarium or carpellary 
envelope, but the ovular coating—that these plants are in fact 
gymnosperms in the sense of having naked nuclei and embryo- 
sacs, not naked ovules. 
P. Van Tieghem, on the contrary, in the Annales des Sciences 
Naturelles, ser. 5, vol. x,, considers the gymnospermy of the 
