146 TYPE STUDIES 



A. General morphology. Well-mounted, herbarium sheets are excellent 

 for this study. Note : 



1. The upright stems, with spirally arranged, needle-shaped leaves. 



2. The long terminal cones, composed of spirally arranged scales 

 (sporophylls). 



3. The creeping stems with leaves similar to those of the upright stems. 



4. The rather infrequent roots. 



Illustrate the above features in a habit sketch. 



B. The cone and its scales, or sporophylls. Examine preserved material. 



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

 (sporophylls) if not illustrated under A. 



2. Cut off several scales and draw one as seen from the inside, showing 

 the large sporangium at its base. 



3. Construct a diagram illustrating the attachment of the scales to the 

 axis of the cone and the way in which they overlap one another. 



The scales are specialized spore leaves, or sporophyllsi What are some of 

 the reasons why they should be so considered ? 



C. The sporangium and its spores. Split a sporangium open and note the 

 immense number of minute spores. Draw a group. What is the sig- 

 nificance of the angles along one side ? Like the spores of the bryo- 

 phytes and pteridophytes generally, they are developed in groups of 

 four, tetrads, from spore mother cells. 



D. The cell structure, or histology of the stem and leajf. This is a profitable 

 but detailed study. 



1. Cut cross sections of the stem. Note the epidermis, the thick corti- 

 cal regions of ground tissue, the vascular strands called leaf traces, 

 leading out to the leaves from the central Jibro-vascular bundle. In 

 the fibro- vascular bundle observe the more or less parallel regions of 

 wood (xylem), composed of large tracheids, and hast (phloem) within 

 the hundle sheath. Draw the details of cell structure in a series of 

 figures from cross and lengthwise sections. 



2. Examine the surface of the leaves for stomata. Cross sections of 

 the leaves will show their simple cell structure. 



E. The germination of spores, and the gametophytes. Gametophytes have 

 not been found in America and the spores have not been germinated 

 beyond the first few cell divisions. The propagation of plants is 

 chiefly by the branching of stems which separate as older parts die 

 away, and in some species by peculiar vegetative buds. 



Reference. Campbell, 23. 



135. Selaginella. Various species of Selaginella have quite differ- 

 ent habits of growth and arrangements of leaves and branches. 



