THE POLYTRICHACE^E OF WESTERN NORTH AMERICA 273 



5. Peris tome wanting. 

 6. Stomates present on capsule. 



7. Capsule terete Bartramiopsis. 



5. Peris tome present. 

 6. Stomates present on capsule. 



7. Capsule terete Dendroligotrichum. 



2. Lamallae on upper side 20 or more. 

 3. Lamina of i layer of cells. 

 4. Leaves not bordered. 

 5. Peristome wanting. 

 6. Stomates present on capsule. 



7. Capsule 2-4 angled Polytrichadelphus. 



3. Lamina of 2 layers of cells. . 

 4. Leaves not bordered. 

 5. Peristome wanting. 



6. Stomates present on capsule. 



7. Capsule keeled on one side, somewhat oval in cross 

 section Lyellia. 



i. Calyptra densely covered with hairs. 

 2. Lamellae wanting. 

 3. Lamina of i layer of cells. 

 4. Leaves not bordered. 

 5. Peristome present. 



6. Stomates wanting on capsule. 



7. Capsule terete Racelopus, 



2. Lamellae on upper side 20 or more. 

 3. Lamina of i layer of cells. 

 4. Leaves not bordered. 

 5. Peristome present. 

 6. Stomates either present or wanting on the capsule. 



7. Capsule terete Pogonatum. 



6. Stomates present on capsule. 



7. Capsule 4-6 angled 1 Polytrichum. 



'The writer has followed the classification of Brotherus in Engler & Prantl: "Die 

 natiirlichen Pflanzenfamilien, " Teil i, Abt. 3, s. 669-698 (1904) except in the separa- 

 tion of Pogonatum from Polytrichum. The chief question here arising is where to 

 put Pogonatum alpinum. Excepting this plant the Pogonatums have capsules terete, 

 teeth 32, stomates wanting; the Polytrichums have capsules angular, teeth 64, stomates 

 present; Pogonatum alpinum is a fine gradation form between the two genera, having 

 the terete capsule of the Pogonatums, the stomates of the Polytrichums, and standing 

 between the two genera in its 32 or 64 teeth depending upon how one counts the doub- 

 ling. Whether one classes it a Pogonatum or a Polytrichum depends upon whether one 

 emphasizes the form of the capsule or the presence of the stomates. When there is 

 nothing to be gained by using a microscopic character in the separation of genera, 

 why not use one which can be seen with the naked eye? In this paper Pogonatum 

 alpinum is therefore classed as a Pogonatum. 



