SELAGINELLA SPOROPHYTE 263 



a. Macrosporangia, which are of a green or 

 light-brown colour, and appear to be of rounded 

 tetrahedral form. 



b. Microsporangia, which are more nearly spheri- 

 cal, and of a reddish -brown colour. 



Note in older cones that the sporangia are already 

 open, dehiscence having taken place in a plane 

 parallel to that of the leaf. 



II. Cut out as thick a piece of the stem as can be 

 found, and about one inch in length : note a central 

 white dot on the transversely cut surface : this is the 

 single central vascular bundle. Slice off the upper 

 surface of the stem with a razor till the whole course 

 of the vascular bundle is laid bare, and observe with 

 a lens 



1. The course of the central vascular bundle, which 

 is directly longitudinal and median. 



2. The smaller lateral bundles, which pass from the 

 central bundle without branching, into the leaves, and 

 traverse the midribs of the leaves. 



III. Cut transverse sections of a well-developed stem : 

 mount some in glycerine, others in chlor-zinc-iodine : 

 others again may be mounted in acid solution of aniline 

 sulphate. Examine first under a low power, using a 

 high power when necessary, and observe the following 

 tissues in succession, starting from the periphery of the 

 section : 



1. At the periphery a layer of small, thick-walled 

 cells, forming an ill-defined epidermis, with no 

 stomata : it is covered externally by a continuous 

 cuticle. Beneath the epidermis, and not clearly 

 marked off from it, is 



