204 A TEXT-BOOK OF BOTANY 
same kind of spores. For example, certain sporangia (usu- 
ally the lower ones) may each contain four large spores 
(Fig. 196, C and D), while the other sporangia contain 
very numerous and very 
much smaller spores 
(Fig. 196, A and SB). 
There may be no differ- 
ence in the appearance 
of the sporangia. <A 
plant that produces two 
kinds of spores, differing 
in size, is said to be he- 
terosporous (spores dif- 
ferent). The appear- 
ance of this condition 
is a very important 
fact, for it is an intro- 
duction to the appear- 
ance of the higher plants. 
Difference in the size 
of spores does not seem 
important; but when 
this is accompanied by 
difference in the gamcto- 
Fic. 196.—Sporophylls of Selaginella, A, spo- phytes produced, it is 
Fonbyl bearing sporangium that preiuees very important. When 
bearing sporangium that produces few the small spore germi- 
large spores (D). 3 
nates, it produces a few- 
celled gametophyte, so small that it is contained entirely 
within the old spore wall. This gametophyte produces 
one antheridium, and this antheridium forms the bulk of 
the whole body. Therefore, the small spore produces a 
very small male gumetophyte. When the large spore ger- 
minates, it produces a many-celled gametophyte, which 
bursts through the spore wall and becomes partly ex- 
