[VOL. 2 



298 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



Rhodophyceae have been worked out in fair detail, although 

 no percentages of absolute accuracy can be given at present. 

 The general results are as follows: 



(1) The greater part of the species are known from one 

 zone of temperature. 



(2) A considerable number of species are known from two 

 zones of temperature. 



(3) A comparatively small number are credited to three 

 zones of temperature. 



(4) Species credited as occurring in four or five zones of 

 unlike temperature are extremely few and almost always 



doubtfully so accredited. 



(5) There is a change of facies of the flora in each suc- 

 cessive zone, i.e., with every increase or decrease of 5°C, 

 excepting in the cases of the Upper Boreal and the Upper 



Austral. 



This means that most species are, so far as known, confined 



to zones of amplitude of 5°C. of summer temperature, that 

 certain species extend over zones representing 10 °C. ampli- 

 tude, while a few may extend over zones representing 15° C. 

 amplitude of summer temperature, and extremely few defin- 

 itely known in zones covering over 20° C. amplitude of sum- 

 mer temperature. 



To mention the results of the preliminary survey of the 

 marine Rhodophyceae so far listed and checked, may give 

 approximate conditions which also seem to exist in other 

 groups. The species and varieties thus far accredited to 

 this group number about 3,350. Of these the northern hemi- 

 sphere has about 34 per cent in its extratropical waters, the 

 southern hemisphere approximately 44 per cent, whilo the 

 tropical waters have approximately 22 per cent. Of the entire 



number, approximately 71 per cent are confined 

 of temperature; about 21 per cent extend over two succes- 

 sive zones of different temperature; about 6 per cent are 

 accredited to three successive zones of different temperature ; 

 while between 1 and 2 per cent are accredited, but with more 

 or less, generally very considerable, doubt, to four, or even to 

 five, successive zones of different temperature. 



