CREATION BY EVOLUTION 



Early in the development of living things one group of 

 plants acquired the ability to manufacture that wonderful 

 substance, chlorophyll, which gives the green colour to all 

 foliage, and these primitive chlorophyll-bearing organisms 



must be regarded as the ancestors of 

 all plant life. 



The simplest chlorophyll-bearing 

 plants to-day are the unicellular 

 green algae, such, for example, as 

 Pleurococcus (Fig. 3). These 

 reproduce only by cell-division. 

 Other green algae, such as green 

 silk, or Spirogyra, reproduce by 

 both cell-division and cell-fusion. 

 The introduction of cell-fusion 



Fig. 3. — Individual plants . i i-r i • • r 



of a simple green alga (Ple»- mto the life histories ot organisms 

 rococcus vulgaris) showing j^-j ^j^^ foundation for the develop- 



reproduction by cell division. 1 1 r • • 



ment of sex, for cell-fusion is 

 the essential process in sexual re- 

 production. 



The modern representatives of 

 the other great groups of chloro- 

 phyll-bearing plants, such as the 

 mosses, ferns, club mosses, little club mosses, and conifers 

 (Figs. 4-7), illustrate definite advances in evolutionary prog- 

 ress, but they do not form a genetical series — that is, they do 

 not bear to each other the relation of ancestor and descend- 

 ant. Some students incline to the opinion that all the great 

 modern groups of plants have descended from one main hypo- 

 thetical fern-like branch, the Prifnofilices, which can be traced 

 back to the dawn of the fossil record but is now extinct. From 

 the Primofilices there descended cycad-like forms (Cycado- 

 filices, cycad- ferns), also now extinct, but known from abun- 



[146] 



The cells tend to remain 

 attached after dividing, thus 

 forming a transition from a 

 unicellular to a multicellu- 

 lar plant. 



Reproduced, by permis- 

 sion, from Gager's Funda- 

 jnentals of Botany, published 

 by P. Blakiston's Sons & Co. 



