Mosses and Lichens 



growing sporogonium, thus the veil of the spore-case is the old 

 archegonium wall. 



Anomodon apicu- 

 latus. Leaf with 

 vein extending to 

 the apex. 



HOW A HAIRY-CAP PROCURES A MAXIMUM AMOUNT 



OF LIGHT 



The leaves of a Polyirichum have many points of interest. 

 It is a recognised law in nature that the position of the leaves 

 of a tree or plant is such as to admit the greatest amount of 

 light and air possible to the great- 

 est number of leaves. Since it 

 is the habit of these mosses to 

 grow perpendicularly with little 

 or no branching and to have the 

 leaves long and slender, the leaves 

 are so placed on the stem as to 

 form a spiral of leaves, every 

 eighth leaf lying directly above 

 the first one counted. If a line 

 be started atone leaf, and wound 

 about the stem joining all eight 

 leaves, it will be found that it 

 has coiled three times about the 

 stem. The leaves joined form 

 "one story." If a plant with 

 several stories of eight leaves 

 each has straight perpendicular 

 lines drawn joining leaves which 

 lie one directly above another, 

 it will be found that the dis- 

 tance between each line is % of 

 the circumference of the stem. 

 The fraction which represents 

 distance will always have for a numerator the 

 number of spirals in a story and will always have for the denomi- 

 nator the number of leaves in a story. In some Polytrichum 

 mosses every thirteenth leaf is directly over the first one counted, 

 so that it would require a spiral of five coils to connect all 

 thirteen and would require the circumference to be divided by 

 thirteen perpendicular lines, each line % of the circumference 



Pogonatwm Alpinum. 

 Upper view showing 

 transparent base 

 and lamelias cover- 

 ing the surface ex- 

 cepting along the 

 serrate margin. 



Ceratodon purfur- 

 eum. Cross section 

 of leaf showing 

 blade one cell 

 thick, and vein 

 several cells thick. 



the horizontal 



