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 dicotyledons, 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 Keichen- 

 bachii 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 



