HOW TO USE THE KEYS 29 



The moss used in the foregoing illustration will serve 

 as an example. Going back to the beginning of the Key, 

 we find that the capsule did not come under consider- 

 ation until we had placed our specimen under *'IL 

 a.," and further, under ''Stems one-half inch long or 

 less," ''Leaves hair-like throughout." Now, suppose 

 we have no capsule to aid us and we cannot tell whether 

 the plant belongs under "Capsule erect" or "Capsule 

 not erect." We must look up all the genera coming 

 under both these heads, which are 1,2, 3, 4, 6, 7, 8, 11, 

 15, 26, 36, 38, and compare with our moss the illustra- 

 tions and descriptions, especially the characteristics in 

 italics, but omit all reference to seta and capsule, i. 

 Trematodon we throw out because the illustration 

 shows the leaves much longer than those of our plant, 

 and it grows on damp soil, whereas we found our plant 

 on dry soil. 2. Ditrichum in one case has leaves too 

 small to be seen easily and in the other species they are 

 again too long. 3. Saelania occurs especially in lime- 

 stone regions, and the leaves are bluish-green, while 

 those of our moss are a rather dark green. 4. Ccratodon 

 corresponds in both illustration and description to our 

 specimen, but to make sure that we are not mistaken 

 we look through the rest of the genera. 6. Dicranella 

 we discard because the leaves turn to one side. 7. 

 Oncophoriis we discard because the leaves are too long 

 and become crisped in drying, while those of our plant 

 fold straight against the stem when dry. 8. Dicranum 

 has leaves turned to one side. 1 1 . Wcisia has leaves too 



