358 PRACTICAL BOTANY 



XIX. Cut transverse sections of the main axis of a plant of 

 Sphagnum, and mount in weak glycerine or glycerine jelly : 

 examine under a low power, and observe 



1. At the periphery of the section two or three irregular layers 

 of cells with thin walls, and no cell-contents : lying internally to 

 these is 



2. A dense brown band of tissue which merges gradually into 



3. A massive central pith, of comparatively large cells, with 

 thin cell- walls and but little protoplasm. 



Examine the peripheral tissues under a high power : round 

 holes will be observed in the cells- walls as seen in surface view, 

 while accurate observation at the points where the longitudinal 

 walls have been cut through will show that these circular mark- 

 ings are actually open pores, by means of which the cavities of 

 the cells of this tissue communicate one with another, and are 

 ultimately in open communication with the medium in which the 

 plant grows. This tissue serves as a capillary system, by means 

 of which water is supplied to the inner tissues of the stem. 



XX. Strip off one or two leaves : mount in water, or very weak 

 glycerine, and examine under a low power : note 



1. The simple form of the leaf, and its entire margin. 



2. The absence of any midrib. 



3. The simple structure, the leaf consisting only of a single 

 layer of cells, amongst which two types may be recognized under 

 a high power, viz. 



a. Large colourless cells, the walls of which are marked by 

 annular or spiral bands, and showing here and there round open 

 pores similar to those already observed in the superficial layers 

 of the stem : these cells have no cell-contents. 



b. Smaller cells of narrow form, easily recognized by their 

 containing green chlorophyll granules embedded in colourless 

 protoplasm : these cells, being attached by their ends one to 

 another, together form a network, the meshes of which are 

 occupied by the large colourless cells, a. 



XXI. It may be found difficult to obtain material for the 

 practical study of the sexual organs of Sphagnum, and it will 

 accordingly suffice here to refer to the descriptions given of them 

 in text-books. 





