32 AN INTRODUCTION TO THE STUDY OF FOSSILS 



knowledge of various plant forms is being constantly supple- 

 mented by discoveries of petrified plants in all stages of growth 

 and with their various parts, such as leaves and stems, still 

 connected as in life. Consideration of these advances of 

 paleobotany indicates that the plant record may soon come 

 to have all the importance in the study of climate, former 

 geographic relationships and evolution that the animal record 

 has. 



Plants are divided, mainly on the basis of their method of 

 reproduction as well as the accompanying development of sup- 

 porting tissue, into four large divisions: — 



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Division I. Thallophyta t^2 



II. Bryophyta 42 



III. Pteridophyta 44 



IV. Spermatophyta 55 



DIVISION I, THALLOPHYTA 



The thallophytes include the most primitive plants, ranging 

 in size from single microscopic cells to seaweeds of enormous 

 dimensions. The forms included in this group agree in their 

 simple structure, being plants in which there is usually little or 

 no differentiation of organs, such as stems and leaves. Such 

 a simple plant body is called a thallus, and the plants distin- 

 guished by possessing this undifferentiated mass of cellular 

 tissue are called the thallophytes or thallus plants (> Greek 

 phyton, a plant). 



The Thallophyta include the following five sub-divisions : — 



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A. Myxomycetae t,3 



B. Schizophyta S3 



C. Diatomeae 34 



D- Algae 35 



E. Fungi 40 



