308 Causes and Course of Organic Evolution 



yellow algse occur in shallower depths up to tide margin where 

 yellow-green rays penetrate; that the green algae occur at or 

 near the surface where red light is averagely strongest; and 

 that blue-green algae would be best adapted to orange-yellow 

 light. 



But, even amongst the variously colored blue-green algae, 

 the variation in species from blue-green to olive-green, from 

 this to greenish yellow, then to greenish broT;\Ti, and from 

 this to brownish or violet-pink and thence to pink-red, is 

 usually correlated with a like environal relation to light rays. 

 Thus the green or the greenish yellow species are mostly met 

 with in exposed situations, and they best resist sun-dessication 

 wlien combined with appropriate fungi to form lichens as 

 in the pleurococcaceous Verrucaria and Lecidium or in the 

 nostocaceous lichen Collema. The blue-green or brown-green 

 forms occur in moister and more shady positions, where they 

 may give rise to such lichens as Peltigera and Ramalina; those 

 wliich show a bro\\iiish red to rose-pink color are marine as 

 in Dermocarpa riolacea and rosea, Pledonema roseolum and 

 P. gelenldnianum, which are found on rocks, on algae, or on 

 sea animals at varying depths. 



So equally for the Cyanophyceae as a group, and for their 

 probable ancestral connection T\dth the green, the brown, and 

 the red algae, that will be discussed later, the color relations 

 indicate that the Cyanophyceae have been a highly adaptable 

 series. 



Confining attention for a time now to the question of chro- 

 matoj^hore evolution, we consider that it is possible to trace 

 here three lines of advance, that represent the green, the brown, 

 and the red algoid groups respectively. 



In the simplest and probably most primitive green algae 

 that are included under the Pleurococcaceae, Tetrasporaceae, 

 and Protococcaceae, the chromatophore is nearly always single, 

 and either occupies the entire circumference of the cell, as 

 in Tetraspora, Oocardium, etc., or is an extensive lateral or 

 posterior expanse as in Dimorphococcus, Chlorocijstis, and 

 Palmophyllum. Or it may be divided into two chlorophyll 

 bands or chromatophores as in Chlorangiuniy or there may be 

 further division into from five to twelve masses as in Oocystis 

 and some stages of Pleurococcus. 



But further, the minute chromatin granules in the chroma- 

 to})hore of the most evolved Cyanophyceae aj^pear now to 

 unite and enlarge into one bright refractive "pyrenoid," and 

 then instead of glycogen the elaborated carbohydrate is de- 

 posited in or round the pyrenoid as starch. Or several pyre- 



