300 



GENERAL BOTANY 



Pith (staring) 



Vascular strand (conducting) 

 Cortex A (storing) 



Meristem 



Leaf 



The young leaves unfold in the spring in the circulate manner 

 represented in Fig. 168 and finally develop a dark, shining, 

 elastic leafstalk, which forks repeatedly to form the compound 

 leaf. The mature leaf is pinnate (like a feather), and the ultimate 

 green divisions are called pinnules. The veins of the pinnules 

 are forked, or dichotomous, like the veins of other ferns, and the 

 edges of the pinnules are reflexed to cover the sporangia which 

 produce the spores. 



The seasonal life of Adiantum corresponds exactly to that of 

 perennial herbaceous seed plants, like the mandrake, which have 



an underground rhizome and 

 -Leaf trace annual aerial parts. The 



leaves manufacture food by 

 photosynthesis ; some of the 

 food is used for the season's 

 growth, while the excess 

 passes down the leaf and 

 into the rhizome, where it 

 is stored for use the next 

 spring. When frost comes, 

 the leaves of the maidenhair 

 die down and the rhizome 

 hibernates and carries the 

 plant over the winter. With 



the advent of spring the reserve food is digested, the young 

 leaves begin to uncoil, and another active period in the life of 

 the plant is begun. In order to carry on these various functions 

 the tissues of the fern stem and leaf are more highly differentiated 

 than those of any plants yet studied except the seed plants. 



Structure. The general arrangement of the main tissues of 

 the rhizome of Adiantum is diagrammatically represented in 

 Fig. 169. In this figure it may be noted that the tissues of the 

 fern stem are the same in kind and general arrangement as that 

 already studied in herbaceous dicotyledons. The outside of the 

 stem is protected by an epidermis and by the thick-walled cells 

 of the outer cortex, which constitute a kind of ezoskeleton for 

 the entire stem. The inner portions of the cortex and pith are 



FIG. 169. Diagram of long section of the 



rhizome, showing the main tissue areas 



and their principal functions 



