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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 B). 

 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 gameto- 

 phytes produced, it is 

 very important. When 

 the small spore germi- 

 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 gametophyte. When the large spore ger- 

 minates, it produces a many-celled gametophyte, which 

 bursts through the spore wall and becomes partly ex- 



FIG. 196. Sporophylls of Selaginella: A, spo- 

 rophyll bearing sporangium that produces 

 numerous small spores (B); C, sporophyll 

 bearing sporangium that produces few 

 large spores (Z)). 



