284 PRACTICAL BOTANY 



semble the transverse sections of the stem in the 

 arrangement of the tissues, though the whole structure 

 is simpler : there are usually only three plates of 

 xylem : these are often complicated by irregularities, 

 e.g. fusion, &c., and are less strongly developed in their 

 central portion than those of the stem. 



If similar sections be cut successively from roots of higher 

 order, they will be found to show successively reduced types of 

 structure, till the xylem is finally represented only by a single 

 group of elements, which is surrounded by tissues of the phloem. 



Median longitudinal sections may be cut through the apices of 

 roots which have been hardened in alcohol : from these it will be 

 seen that there is a stratified structure of the apical meristein, in 

 which may be recognized a distinct root-cap, marked off from 

 the layers below it by a layer of dermatogen, which can be 

 traced as a continuous layer beneath the root-cap : centrally a 

 distinct strand of plerome may be recognized. Bifurcations may 

 be found in such sections, showing that the branching is a true 

 dichotomy, 



IX. Cut median longitudinal sections through a cone, 

 bearing mature sporangia : mount in glycerine, and * 

 examine under a low power : observe the structure of 

 the axis as before seen in longitudinal section, with a 

 vascular system sending out branches into the leaves : 

 the chief difference between this and the vegetative 

 axes is the presence of sporangia. Note 



i. That one sporangium is seated with a short stalk 

 on the upper surface of each leaf. 



ii. That no branch of the vascular system enters the 

 stalk of the sporangium. 



iii. That the cavity of the sporangium is surrounded 

 by a thin wall. 



iv. That the cavity thus inclosed may be filled with 



