THE. LIFE-HISTORY OF A FERN 



SPORE 



Fern-Plant. If the events above detailed recur in regular succession 

 there will be seen a regular alternation of two phases of life, or generations : 

 of these the one, the prothallus, bears the sexual organs, which contain 

 the sexual cells or gametes, and it may accordingly be styled the 

 gametophyte : the other, the Fern-Plant, is non-sexual or neutral, and bears 

 the sporangia, containing the spores : accordingly it may be styled the 

 sporophyte. The study of Ferns at large leads to the conclusion that this 



regular alternation of generations 

 is typical for the family. These 

 two alternating generations differ 

 not only in form, but also in 

 their relation to external circum- 

 stances, and especially in the 

 water-relation. The sporophyte 

 is structurally a land-growing 

 plant, with nutritive, mechanical, 

 and conducting tissues, and a 

 ventilating system : not only is 

 it capable of undergoing free 

 exposure to the ordinary atmo- 

 spheric conditions, but dryness 

 of the air is essential for the 

 final end of its existence, viz. 

 the distribution of the spores. 

 On the other hand, the gameto- 

 phyte is structurally a plant 

 ill-fitted for exposure, with un- 

 differentiated and ill-protected 

 tissues, and no ventilating 

 system, while the object of its 

 existence, viz. the fertilisation 

 carried out by the sexual organs, 

 can only be achieved in the 

 presence of external fluid water. 



There is thus a marked difference between these two phases, and their 

 sequence may be said to constitute an antithetic alternation. As regards 

 the water-relation, the whole life-cycle of the Fern might not inaptly 

 be designated as amphibious, since the one phase is dependent on 

 external fluid water for achieving its object of propagation, while the 

 other is independent of it. 



It will be seen in the next chapter that this is not a condition for 

 Ferns alone, but that such alternation as is seen here has its parallel in 

 many other plants, though with great differences in detail, and especially 

 in respect of the balance of size of the two generations. 



FIG. 16. 

 Scheme of life-cycle of a Fern. 



