Lecture XX. 167 



through the foot from the parent garnetophyte ; but when connec- 

 tion has been established between the new plant and the soil by 

 means of the root, and when its carbon supply is secured by its 

 first leaf, food from the garnetophyte becomes superfluous and the 

 garnetophyte gradually shrivels away. Meanwhile the new plant 

 develops new and larger leaves, its stem waxes stronger, additional 

 roots from its base are produced, and it is soon recognisable as a 

 young fern-plant. 



The structure of these organs resembles that of the organs of the 

 mature plant ; the conducting system, however, is less complicated 

 in its formation, and in the young stem appears as a single core of 

 wood surrounded with bast. As the stem strengthens, this core 

 branches and forms the conducting net-work which is characteristic 

 of the mature parts of the stem. 



All the leaves of the young plant are at first simply nutritive in 

 their function, supplying carbohydrates by photo- 

 synthesis and raising the transpiration-current. 

 Spore-producing leaves sporophylls are only 

 produced later. 



From the life-history just described, it is evi- 

 dent that the fern-plant is a sporophyte compar- 

 able to the sporophyte of Marchantia or of 



Funaria, but so constructed that it is able to FlG Aspidium 



carry on an independent life in all but its initial filix-'mas, game- 

 stages. It is fitted for a wholly terrestrial exist- tophyte with 



ence, and we have seen how the complicated ypung s P r ~ 

 f . , r . . . phyte attached, 



structure of its leaves, stems and roots enable it, ^ ^ 



though living in sub-aerial conditions, to carry 



on its life-processes, which are similar to those discharged by the 



submerged organs of aquatic plants. 



For the ripening and dissemination of the spores dry conditions 

 are essential. But the germination of the spores and the growth of 

 the garnetophyte demand conditions of moisture. Furthermore, 

 the garnetophyte resembles the submerged thallophytes in its water 

 requirements more than it does the land-plants. For the success- 

 ful formation of its gametes and for the process of fertilisation 

 aquatic conditions are imperative. Looked at from this point of 

 view the fern is properly described as amphibious. Its sporophyte 

 generation is distinctly terrestrial while its garnetophyte generation 

 is almost entirely aquatic. Comparing its life-history with those of 

 the forms which we have already studied we see that the importance 

 of the sporophyte in the life-cycle is in proportion to the extent to 

 which the plant has withdrawn from aquatic and taken to terrestrial 

 conditions. 



