FEBRUARY 1, 1901.] 
plants, when properly studied, is, from the 
close relation of plants to their stations and 
climates, even more valuable than that of 
animals.”” But he very appropriately adds 
the caution that “In pursuing such in- 
quiries, we should have some definite views 
as to the nature and permanence of specific 
forms, whether with reference to a single 
geological period or to successive periods.”’ 
Balfour had already pointed out the 
necessity for a wide acquaintance with 
plant distribution in order to apply fossil 
plants with any success as tests of climate, 
and Renault in 1881, expressed views sim- 
ilar to those held by Dawson, when he 
pointed out that plants were superior to 
animals as a test of climate because of 
their relative fixity, and therefore more 
permanent relations to their environing 
conditions—the ability to migrate render- 
ing animals an uncertain guide. 
While their relative fixity is an element 
which imparts a special value to plants in 
this respect, it must nevertheless be recog- 
nized that influences such as long rivers 
with a northerly and southerly course, are 
likely to introduce a disturbing element by 
reason of their causing a mingling of the 
floras of dissimilar climates, and for this 
and other reasons it is generally conceded 
that drift material must be carefully ex- 
eluded from all considerations which in- 
volve questions of climate. 
Variations in the soil, exposure to light, 
humidity of the atmosphere and many other 
conditions which tend to promote structural 
and functional modifications, and eventu- 
ally also type alterations, must be carefully 
weighed and that these elements have been 
as important factors in the past, as they are 
at the present day, cannot be doubted 
when we recall the profound modifications 
exhibited by the various floras of Paleozoic 
time, and the fact, to which Lesquereux has 
directed attention, that ‘‘A single modifica- 
tion of the character of the vegetation gen- 
SCIENCE. 
167 
erally follows great geological disturbances 
which produce permanent changes in the 
atmospheric condition of a country.” 
In 1872 Saporta pointed to the deter- 
mining influence of atmospheric conditions, 
and showed that the relative preponder- 
ance of the monocotyledons and dicotyle- 
dons could be referred to conditions of 
humidity in such a way that the former 
increase while the latter decrease when the 
humidity becomes general, or with a dimi- 
nution.of temperature ; and that, in conse- 
quence, a dry and warm climate favors a 
larger proportion of dicotyledons than a 
warm and moist, or a cold and moist cli- 
mate. With these considerations in mind, 
we cannot avoid the conviction that the 
modern science. of ecology as expounded 
by Warming and Schimper, and as ex- 
ploited on this side of the Atlantic by Ga- 
nong and others, must throw much light 
upon questions of this kind by giving ac- 
curate data upon which to base comparative 
studies. 
The peculiar conditions under which 
plants pass into the fossil state render it an 
altogether exceptional circumstance to find 
all parts present. This is more particularly 
true of those more delicate tissues and or- 
gans which constitute the structure of the 
gametophyte, but it also applies with con- 
siderable force. to all the soft parts of the 
sporophyte. Important exceptions to this 
rule nevertheless appear. Renault has al- 
ready shown that in Cordaianthus, the mi- 
crospores are to be seen in position within 
the canal of the archegonium, as also in the 
pollen chamber, and they exhibit very 
clearly the development of the prothallus. 
He has also observed similar conditions of 
preservation in various Calamarieae. More 
recent investigations have also given an- 
other important example of this kind in 
Parka decipiens, the remains of which show 
prothalli and both kinds of spores, and, 
coming as it does from the Devonian, it 
