SELAGINELLA 147 



S. rupestris is generally the most available of our native species, 

 but S. opus is often easily obtained. S. Kraussiana is a delicate 

 form frequently cultivated in conservatories. S. Martensii and 

 other tropical species are large, erect, much-branched, ornamental 

 plants cultivated in greenhouses, and when in good fruit are ex- 

 cellent for type study. A single plant in fruit will supply a large 

 class with material, but the smaller species are also good. 



A. General morphology. Note : 



1. The character of the stems, upright or creeping. Describe 

 their method of branching, generally in one plane. 



2. The scale-like leaves. These are spirally arranged in some 

 species (as S. rupestris), but in other forms are distributed 

 in four rows and are of two sizes. What is their arrange- 

 ment in the type studied ? Have the stems an upper and 

 lower side (dorsiventral symmetry) ? What advantage is 

 there in this symmetry in relation to the spreading habits 

 of growth ? Search for a very small triangular structure, 

 called the ligule, at the base of the leaf. Its significance 

 is not known. 



3. The spike-like cones composed of crowded scales (sporo- 

 phylls). How are these arranged ? How many rows ? 

 What is the geometrical form of the cone ? 



4. The fibrous forking roots. In tropical species roots may 

 be developed from the tips of special descending branches 

 (rhizophores). 



Illustrate the above points in habit sketches, paying special 

 attention to the arrangement of the leaves on the stem. 



B. The cone and its scales, or sporophylls. 



1. Draw a cone in detail, showing the arrangement of the 

 scales, or sporophylls (if not illustrated under A). 



2. Note the sporangium attached at the base of each sporo- 

 phyll. Are the upper and lower sporangia of the same 

 cone alike ? Cut off the scales and compare them, dis- 

 tinguishing between oval sporangia containing minute 

 spores, microspores, and larger-lobed sporangia containing 



