THE LIFE-HISTORY OF A FERN 



[CH. 



more deeply seated, as in the root, while in the leaf they follow the course 

 of the vascular strands. These give to the several parts increased mechanical 

 strength, while their thickened walls have also a special power of retaining 

 water within their substance. 



Thus constituted the Male Shield Fern is an organism which is capable 

 of leading an independent life on exposed land-surfaces. It is in a position 

 to nourish itself by taking up from the soil the water and salts which it 

 requires, and to elaborate therefrom, and from the carbon-dioxide of the 

 air, fresh supplies of organic food. Further, though it is frequently found 



Fig. 3. Transverse section of rhizome of Bracken Fteriduiin aqiiilinuin, 

 showing the outer and inner series of meristeles, antl the irregular 

 Vjands of sclerenchyma between them. These are embedded in soft 

 ground-parenchyma, with a hard sclerotic rind. ( x 10.) 



growing in situations where moisture is abundant and the air moist, still it 

 can resist considerable drought, and is capable of living under as exacting 

 conditions as any ordinary terrestrial plant. 



For comparative purposes the vascular tissues, which are so marked a 

 feature of land-living plants generally, are those which command the greatest 

 attention. For the study of the tissues composing a vascular strand, or 

 nieristele as it is called, a rhizome with long internodes, such as the Bracken, 

 gives the best results. In a transverse section of it taken between the leaf- 

 insertions, an outer and an inner series of vascular .strands are found, separated 



