ATRICHUM UNDULATUM. 87 



C. THE STEM. Notice * 



1. The size and shape. 



Remove the leaves near the base, mount a transverse sec- 

 tion, and notice 



2. The outline of the section. 



3. The three tissue regions ; the peripheral brown tissue, 

 the axial tissue forming a light spot in the center, and 

 the intermediate colorless tissue. 



1). THE LEAVES. Notice 



1. The manner of arrangement on the stem. 



2. The difference in size on different parts of the stem. 



3. The shape of 



a. The lowest, scale leaves. 



b. The middle, foliage leaves. 



c. The uppermost on flowering stems, forming the 

 outer portion of the head, perichsBtial leaves. 



4. The structure ; a thin lamina, with a thicker median 

 line, the midrib. 



5. The character of the margin, especially toward the 

 apex. 



6. In the foliage leaves, the undulations passing obliquely 

 outward from the midrib to the margin ; their absence 

 in the other sorts. 



7. Draw a leaf of each sort scale, foliage and perichaetial. 

 E. THE FLOWERING HEAD. 1 



i. The male heads. Notice 



i Called the" receptacle" by Sachs (Text-book, 2nd Eng. ed., p. 370), 

 but this term has long been in use for the end of the stem on which the 

 parts of a flower are seated. The analogy of the several parts of the 

 moss " flower" to those of the head of a composite (e. g. sunflower) has 

 determined the use of corresponding terms. 



