[E26]

March 23d. 1861. Suppose world shortly before Glacial to have had present temperature; but we know before that it was hotter. Probably the effect of this then would have been an Equatorial Flora, which could live only in hottest regions; & in N. Tropical & S. Tropical Flora fitted for less intense Heat, & distinct from each other, for they must have been separated from each other for long time by Equatorial Flora. During Glacial period, I suppose Equatorial Flora almost wholly annihilated, and to N. & S. Tropical flora, which would both have suffered quite so much under Equator during Glacial period, to have occupied Equatorial regions. Their commingling would have made a rich flora, & which now has become accustomed to rather hotter climate than that to which they were accustomed, previously to Glacial period.

35° North

N. Tropical Flora

20° N.

Equator

Equatorial Flora nearly all exterminated during Glacial period.

20° S.

S. Tropical Flora distinct from north

35° S.

over

 

[E26v]

All this upset by Mr Bates paper.

Can species have been very largely developed since glacial period.

Certainly from Lat 25° to Equator productions here ought to have very uniform character.

How is this?

In S. America immigration must have been almost exclusively by lines of mountains.

Growing difficulty is why equatorial production not all destroyed as climate some of temperate must have been best fitted for sub-tropics productions - Probably was & our [best] Temperate productions were sub-tropical before glacial. All Fauna & Flora most disturbed & a few temperate forms crossed owing to disturbance taking advantage of high land.

With respect to S America we have but [many words illeg] is greatest difficulty - Undoubtedly there is much to explain as yet