222 FOREST LANDS OF NORTHERN RUSSIA. 
the only indices upon which one can rely in admitting 
the influence of a climate already colder in the extreme 
north, in Europe, or in America, since the upper chalk. 
But the diffusion of the Magnolia, then present everywhere, 
the abundance of plane-trees, and the presence of a beech 
tree in America, would seem rather to favour the supposi- 
tion of a very great equality in what are precisely those 
the floral parts of which have experienced least of reduc- 
tions and adhesions of parts; in them the primitive axis, 
the contraction of which has given birth to the floral 
formation, is still recognisable, and the phyllotaxis, or 
order of arrangement of the accessory elements of this 
axis is still perceptible, at least, partially in the spiral 
disposition affected by the sexual organs, and even by the 
modified leaves which surround them. The greater part 
of dicotyledonr, not the first doubtless, but at least the 
more remote from the point of original departure, have 
stipules ; and the sheathing petiole of the arales, the long- 
prolonged limb of the petiole of the Credneria, and the 
frequency of the palminerved arrangement, or a tendency 
towards this arrangement, are in our eyes so many indices 
of an anterior state of the foliaceous organs towards which 
the phylloid floral formations of certain types are perhaps 
only a partial recurrence; so that the stipules appear to 
constitute a last vestige of these. It is then probable 
that the dicotyledons, at the time when we encounter 
them for the first time, had already been subjected to a 
long series of modifications. Many of them have taken 
upon themselves in the course of this progression, abor- 
tions and adhesions, secondary variations, the effacement 
of certain characteristics and conditions of climate to the 
north, as to the south, of the Polar Circle. 
‘It is certain that the immense extension which certain 
forms obtained at this epoch, such as the Sequoia Reichen- 
bachit and the Gleichenia, militate in favour of a like 
equalisation of temperature extending from one extremity 
of our hemisphere to the other, and there, perhaps, lies the 
whole secret of the rapid development and the general 
