NEPHRODIUM SPOROPHYTE 171 



combining this result with that obtained by examination of 

 the longitudinal sections the form of the whole cell must be a 

 three-sided pyramid. (Compare Fig. II.) 



2. The segments are arranged in regular order round it, and 

 are cut off successively from the three sides. 



3. Note the mode in which the several segments are further 

 divided. 



Next examine a section which has passed through the root- 

 cap immediately above the apical cell : this will include the 

 young segments cut off from the base of the apical cell by 

 transverse walls, and destined to form the root-cap. Note the 

 first divisions of these segments by walls arranged crosswise : 

 it may be seen that these walls do not coincide in position in 

 successive segments. 



The Leaf. 



XV. Cut transverse sections of a pinna of a leaf of the Male 

 Fern which has no sori upon it : mount in weak glycerine, and 

 observe with a low power that the outline of the section shows 

 the leaf to be of equal thickness throughout, except where 

 traversed by vascular bundles : at those points the pinna is 

 thickened, the lower surface projecting convexly. 



Examine with a high power, and observe successively the 

 following tissues, starting from the upper surface : 



1. A regular epidermis with a thin cuticle : the epidermal 

 cells contain chlorophyll : there are no stomata. 



2. The mesophyil consists in its upper part of thin- walled 

 cells containing chlorophyll, and with small intercellular spaces ; 

 this passes by gradual transition into the lower part, where the 

 intercellular spaces are larger, and the form of the cells less 

 regular. Internal glandular hairs are frequently to be found in 

 the intercellular spaces of the mesophyil. 



3. The lower epidermis, the cells of which also contain 

 chlorophyll : numerous stomata are present : note the form of 

 the two guard-cells as seen in transverse section, and their 

 position in relation to the epidermis. 



4. Here and there vascular bundles, of circular appearance 



