208 



A TEXT-BOOK OF BOTANY 



fourth differs from them all in producing seeds, and hence 

 is called Spermatophytes or seed-plants. It may be well 

 to give certain prominent characters that will serve to dis- 

 tinguish these four primary groups. It must not be sup- 

 posed that these are the only characters, or even the most 

 important ones in every case, but they are convenient for 

 our purpose. 



(1) Thallophytes. Thallus body, but no archegonia. 



(2) Bryophytes. Archegonia, but no vascular system. 



(3) Pteridophytes. Vascular system, but no seeds. 



(4) 'Spermatophytes. Seeds. 



It will be noticed that for each of the first three groupt 

 two characters are given, one a positive character that 



belongs to it, the 



~ iwswL other a negative 



character that dis- 

 tinguishes it from 

 the group above, 

 and becomes the 

 positive charac- 

 ter of that group. 

 For example, thal- 

 lus bodies are 

 found among Bryo- 

 phytes, and the pro- 

 thallium of a Fern 

 is a thallus body; 

 but plants whose 

 thallus bodies do 

 not bear arche- 

 gonia are Thallo- 

 phytes. Also, arch- 

 egonia are produced by Pteridophytes as well as by 

 Bryophytes, but archegonium-bearing plants without a 

 vascular system can be only Bryophytes. Both Pteri- 



FIG. 198. A cycad with columnar stem. After STRAS- 



BURGER. 



