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 groups 
two characters are given, one a positive character that 
belongs to it, the 
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 
Fig. 198.—A cycad with columnar stem.—After Srras- Het " bear _arche- 
BURGER. 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- 
