A TRICHUM UND ULA TUM. 97 



/-. Illustrate the arrangement of the tissues as seen 



in longitudinal section by a diagram. 

 Take a nearly mature capsule, remove the thinnest pos- 

 sible slice from the side of the operculum with the razor 

 inclined toward the beak ; the next slice will include a por- 

 tion of the peristome, in which notice 



/. The rows of cells from which the teeth are 

 formed, and their manner of thickening. Draw. 

 Make several transverse sections through the rim and 

 operculum, and study 



m. The formation of the teeth from groups of cells. 

 Take a mature capsule, mount a number of entire teeth, 

 and notice 



//. The shape and structure of the teeth. Draw. 

 o. Flatten out a calyptra, and observe the cellular 

 structure, especially at the apex. Draw some 

 of the cells. 



3. The mature spores ; note under high power 

 a. The shape. 

 A The wall and contents. 



ANNOTATIONS. 



The step from Marchantia to Atrichum is not so 

 great as that which intervenes between the several 

 preceding examples, and yet the advancement is well 

 marked and especially significant. With the upright 

 growth of Atrichum is correlated the disposition of the 

 leaves and root-hairs. The leaves being green, relieves 

 the stem of its assimilative duties, and in consequence 

 the smaller size and greater firmness better meet the 

 requirements. The root-hairs simulate true roots even 



