Mosses and Lichens 



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

 archegonium wall. 



HOW A HAIRY-CAP PROCURES A MAXIMUM AMOUNT 



OF LIGHT 



The leaves of a Polytriclmm 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 the apex. 

 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 c l <* P 



eum. Cross section 



Anomodon apicu- 

 lattis. Leaf with 

 vein extending to 



lie one directly above another, 

 it will be found that the dis- 



of leaf showing 

 blade one cell 

 thick, and vein 



Pogonatum Alpinum. 



Upper view showing 



Vansparent base tanCC between each line is 3/9, Of several cells thick. 



and lamella cover- r r ^i 



ing the surface ex- the circumference of the stem. 

 cepting along the The fraction which represents the horizontal 

 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 Polytriclmm 

 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 fV f the circumference 



42 



